Image exposure apparatus

ABSTRACT

An image exposure apparatus includes: a spatial light modulating element, constituted by a plurality of pixel portions for individually modulating light irradiated thereon; a light source, for irradiating light on the spatial light modulating element; and a focusing optical system. The focusing optical system includes: an optical system, for focusing an image borne by each of the pixel portions; and a micro lens array, in which a plurality of micro lenses into which the light beams modulated by the pixel portions enter individually are provided in an array. The micro lens array is provided in the vicinity of a focusing position of the pixel portions by the focusing optical system. Each micro lens of the micro lens array has different powers in two directions within a plane perpendicular to the optical axis, to correct aberrations caused by anisotropic distortions in the pixel portions.

TECHNICAL FIELD

The present invention relates to an image exposure apparatus.Particularly, the present invention relates to an image exposureapparatus that causes light, which has been modulated by a spatial lightmodulating element, to pass through a focusing optical system, to focusan image represented by the light onto a photosensitive material,thereby exposing the photosensitive material.

BACKGROUND ART

There are known image exposure apparatuses that cause light, which hasbeen modulated by a spatial light modulating element, to pass through afocusing optical system, to focus an image represented by the light ontoa photosensitive material, thereby exposing the photosensitive material.This type of image exposure apparatus basically comprises: a spatiallight modulating element, constituted by a plurality of pixel portionsfor individually modulating light irradiated thereon according tocontrol signals; a light source for irradiating light onto the spatiallight modulating element; and a focusing optical system, for focusing animage represented by the light modulated by the spatial light modulatingelement onto a photosensitive material. Note that Japanese UnexaminedPatent Publication No. 2004-001244 and A. Ishikawa, “ShorteningDevelopment and Adaptation to Mass Production byMaskless Exposure”,Electronics Mounting Technology, Vol. 18, No. 6, pp. 74-79, GichoPublishing & Advertising Co., Ltd., 2002 disclose examples of imageexposure apparatuses having the basic construction described above.

In this type of image exposure apparatus, LCD's (Liquid Crystal Displayelements), DMD's (Digital Micro mirror Devices), and the like arefavorably employed as the spatial light modulating element. Note that aDMD is a mirror device constituted by a great number of micro mirrorsthat change the angle of their reflective surfaces according to controlsignals, arranged two dimensionally on a semiconductor substrate such asa silicon substrate. In the DMD's, the micro mirrors function asreflective pixel portions of the spatial light modulating element.

It is often required that an image to be projected onto thephotosensitive material be magnified, in the aforementioned imageexposure apparatuses. In these cases, a magnifying focusing opticalsystem is employed as the focusing optical system. If the light whichhas been modulated by the spatial light modulating element is simplycaused to enter the magnifying focusing optical system, the condensingof each pixel portion of the spatial light modulating element becomesmagnified. This causes the pixel size of the projected image to becomegreater, and the image resolution decreases.

Therefore, a configuration is being considered, wherein: a firstfocusing optical system is provided within the optical path of thelight, which has been modulated by the spatial light modulating element;a micro lens array, in which micro lenses that correspond to each pixelportion of the spatial light modulating element are arranged in anarray, is provided at the focusing surface of the focusing opticalsystem; and a second focusing optical system, for focusing the imagerepresented by the light modulated by the spatial light modulatingelement onto a photosensitive material or a screen, is provided withinthe optical path of the light which has passed through the micro lensarray. By adopting this configuration, the first and second opticalsystems enable magnified projection of the image. In this configuration,the size of the image projected onto the photosensitive material or thescreen is magnified. Meanwhile, the light that propagates from eachpixel portion of the spatial light modulating element is condensed byeach micro lens of the micro lens array. Therefore, the pixel size (spotsize) within the projected image is maintained to be small, therebymaintaining the sharpness of the image.

Note that Japanese Unexamined Patent Publication No. 2001-305663discloses an example of an image exposure apparatus that employs a DMDas the spatial light modulating element, combined with a micro lensarray.

Japanese Unexamined Patent Publication No. 2004-122470 discloses thesame type of image exposure apparatus, comprising: a micro lens array;and an aperture array (apertured plate) having apertures (openings)corresponding to each of the micro lenses in the micro lens array,provided behind the micro lens array. By adopting this configuration,only light which has passed through the corresponding micro lens passesthrough the apertures. In this configuration, each of the apertures ofthe aperture plate prevent light from micro lenses adjacent to the microlens that corresponds to the aperture from entering thereinto.Therefore, the entry of stray light into adjacent pixels can besuppressed. In addition, there are cases that slight amounts of lightenter an exposure surface, even when the pixels (micro mirrors) of theDMD are turned OFF such that light does not irradiate the exposuresurface. However, by adopting this configuration, the amount of lightthat enters the exposure surface when the DMD pixels are in an OFF statecan be reduced.

However, in image exposure apparatuses such as those described above,astigmatic differences are generated among light beams, which arecondensed by the micro lenses of the micro lens array after beingmodulated by the pixel portions of the spatial light modulating element,causing the light beams to become oval in cross section. As a result,small pixel sizes cannot be maintained in projected images, and thesharpness of the projected images are deteriorated. The astigmaticdifferences are mainly caused by distortions in the surfaces of thepixel portions of the spatial light modulating element. In the case thata DMD is employed as the spatial light modulating element, the maincause of the distortions is the distortions of the reflective surfacesof the pixel portions of the DMD.

Particularly in the case that anisotropic distortions, in which thereflective surfaces of the pixel portions are rotationally asymmetricalwith respect to the optical axis, are present, the optical systemgenerates astigmatic aberrations. In this case, the light beams whichare condensed by the micro lenses via the reflective surfaces of thepixel portions have different beam waist positions (the position in thedirection of the optical axis at which the beam diameter is minimal),depending on the direction within planes perpendicular to the opticalaxes thereof.

Specifically, if the directions within a plane perpendicular to anoptical axis are designated as an X direction and a Y direction, thebeam diameter in the Y direction is not minimal at the beam waistposition in the X direction, at which the beam diameter in the Xdirection is minimal. That is, the cross sectional shape of the lightbeam becomes an oval. Similarly, the beam diameter in the X-direction isnot minimal at the beam waist position in the Y direction, at which thebeam diameter in the Y direction is minimal, and the cross sectionalshape of the light beam becomes an oval. Because an image is focusedonto the photosensitive material two dimensionally, if these light beamsare employed as they are to form the image, the sharpness thereofdeteriorates.

The above phenomenon is conspicuous when the reflective surfaces of thepixel portions have powers of different signs in two differentdirections within a plane perpendicular to an optical axis, whichbecomes a problem during obtainment of highly detailed images.

A reflective surface, which has been designed to be of a predeterminedcurved surface and in which an unintended distortion occurs, is anexample of a reflective surface of a pixel portion which is rotationallyasymmetrical. This type of reflective surface commonly has differentpowers of the same sign. In this case as well, the aforementionedastigmatic aberration occurs, and deterioration of image sharpness isunavoidable.

Meanwhile, the conventional image exposure apparatus comprises: thespatial light modulating element that has reflective pixel portions suchas the aforementioned DMD; the micro lens array; and the focusingoptical system. This conventional image exposure apparatus is configuredsuch that the focusing optical system focuses the images of the pixelportions (micro mirrors), and such that each micro lens of the microlens array is positioned at the focusing position of a pixel portion.

However, the relative positional relationship between the spatial lightmodulating element and the micro lens array must be maintained in astrict predetermined relationship. Otherwise, problems, such asdecreases in light utilization efficiency and extinction ratios, becomemore likely to occur. Hereinafter, this point will be described indetail.

The areas denoted by reference numeral 100 in FIG. 48A represents apixel portion of the spatial light modulating element, that is, theimage of a micro mirror of a DMD, for example. Reference numeral 101 inFIG. 48B denotes a micro lens array 101, in which micro lenses 102 areprovided. When the micro mirror image 100 is focused onto the micro lensportion 102 of the micro lens array 101, if the micro mirror image 100is focused to be larger than the size of the micro lens 102, the stateillustrated in FIG. 49A occurs. If the spatial light modulating elementand the micro lens array are shifted in a direction that intersects withthe optical axes of the light beams, the state illustrated in FIG. 49Boccurs, and a great amount of eclipse is generated. In these cases, thelight, which has been reflected at the peripheral portions of the micromirrors, is not utilized for image exposure, and the light utilizationefficiency becomes low.

In many cases, masks for shielding unnecessary light are provided at theexteriors of the peripheral edges of the micro lenses 102, eitherintegrally therewith or separately. In the case that a mask is provided,the eclipsed light is shielded thereby. Even if a mask is not provided,the eclipsed light misses the apertures of the micro lenses 102 and isnot condensed thereby, and therefore is not utilized for the intendedpurpose.

Further, if the degree of shifting such as that illustrated in FIG. 49Bbecomes great, a portion of a micro mirror image 100 intended to befocused on a micro lens 102A may be focused onto an adjacent micro lens102B. If light which is to pass through the micro lens 102B is to becompletely shut out, the extinction ratio decreases, because light whichis intended to pass through the micro lens 102A enters thereinto.

DISCLOSURE OF THE INVENTION

The present invention has been developed in view of the foregoingcircumstances. It is a first object of the present invention to providean image exposure apparatus that enables obtainment of highly detailedimages, even in the case that anisotropic distortions are present withinpixel portions of a spatial light modulating element.

It is a second object of the present invention to provide an imageexposure apparatus that enables obtainment of highly detailed images,even in the case that pixel portions of a spatial light modulatingelement have powers of different signs in two directions within a planeperpendicular to optical axes.

It is a third object of the present invention to provide an imageexposure apparatus that enables obtainment of highly detailed images,even in the case that pixel portions of a spatial light modulatingelement have different powers of the same sign in two directions withina plane perpendicular to optical axes, while maintaining a high lightutilization efficiency and a high extinction ratio.

A first image exposure apparatus according to the present inventioncomprises:

a spatial light modulating element, in which a plurality of pixelportions for individually modulating light irradiated thereon accordingto control signals are provided;

a light source, for irradiating light onto the spatial light modulatingelement; and

a focusing optical system for focusing an image borne by the modulatedlight onto a photosensitive material, including: an optical system forfocusing light beams which have been modulated by each of the pixelportions of the spatial light modulating element, to focus the image ofeach pixel portion; and a micro lens array, in which a plurality ofmicro lenses into which the light beams modulated by the pixel portionsand passed through the optical system enter individually are provided;

the micro lens array being provided in the vicinity of the position atwhich the images of the pixel portions are focused by the opticalsystem; and

each micro lens of the micro lens array having different powers in twodirections within a plane perpendicular to the optical axis of the lightbeam that enters thereinto, in order to correct aberrations due toisotropic distortions of the pixel portions.

Note that the “vicinity of the position at which the images of the pixelportions are focused by the optical system” refers to a position z alongthe direction of the optical axis. The position z is within a range thatsatisfies the inequality:

−f/5+zf≦z≦f/5+zf

wherein: f is the focal distance of the optical system; and zf is theposition at which the images of the pixel portions are focused by theoptical system.

A second image exposure apparatus according to the present inventioncomprises:

a spatial light modulating element, in which a plurality of pixelportions for individually modulating light irradiated thereon accordingto control signals are provided;

a light source, for irradiating light onto the spatial light modulatingelement; and

a focusing optical system for focusing an image borne by the modulatedlight onto a photosensitive material, including: an optical system forfocusing light beams which have been modulated by each of the pixelportions of the spatial light modulating element, to focus the image ofeach pixel portion; and a micro lens array, in which a plurality ofmicro lenses into which the light beams modulated by the pixel portionsand passed through the optical system enter individually are provided;

the pixel portions having powers of different signs in two directionswithin a plane perpendicular to the optical axis of the light beam;

the micro lens array being provided at a separated condensing position,which is offset from a position at which the images of the pixelportions are focused by the optical system; and

each micro lens of the micro lens array having different powers in twodirections within a plane perpendicular to the optical axis of the lightbeam that enters thereinto, in order to correct aberrations due to thepowers of different signs of the pixel portions.

A third image exposure apparatus according to the present inventioncomprises:

a spatial light modulating element, in which a plurality of pixelportions for individually modulating light irradiated thereon accordingto control signals are provided;

a light source, for irradiating light onto the spatial light modulatingelement; and

a focusing optical system for focusing an image borne by the modulatedlight onto a photosensitive material, including: an optical system forfocusing light beams which have been modulated by each of the pixelportions of the spatial light modulating element, to focus the image ofeach pixel portion; and a micro lens array, in which a plurality ofmicro lenses into which the light beams modulated by the pixel portionsand passed through the optical system enter individually are provided;

the pixel portions having powers of the same sign and differentmagnitudes in two directions within a plane perpendicular to the opticalaxis of the light beam;

the micro lens array being provided at a separated condensing position,which is offset from a position at which the images of the pixelportions are focused by the optical system; and

each micro lens of the micro lens array having different powers in twodirections within a plane perpendicular to the optical axis of the lightbeam that enters thereinto, in order to correct aberrations due to thepowers of different magnitudes of the pixel portions.

Note that in the first through third image exposure apparatuses above,the micro lenses are not limited to being refractive lenses, and may begradient index lenses or diffraction lenses. As a further alternative,the micro lenses may be structured by combining at least two of:refractive lenses; gradient index lenses; and diffraction lenses. Here,“combining” refers not only to cemented lenses, but also to singlelenses which have been imparted with a plurality of functions. Forexample, a Fresnel lens is a combination of a refractive lens and adiffraction lens. As another example, a spherical lens having arefractive index distribution is a combination of a refractive lens anda gradient index lens.

It is preferable that a configuration is adopted, wherein the imageexposure apparatuses further comprise:

a condensing micro lens array, in which a plurality of micro lenses forindividually condensing the light beams which have propagated theretovia each of the pixel portions are provided, is provided at a separatedcondensing position of the pixel portions, the optical system, and themicro lens array, which is offset from a position at which the images ofthe pixel portions are focused by the optical system.

It is preferable for the condensing micro lens array to be movable inthe direction of the optical axes of the light beams.

It is desirable for a configuration to be adopted, wherein the imageexposure apparatuses further comprise:

an aperture array, in which a plurality of apertures for individuallytransmitting the light beams which have propagated thereto via each ofthe pixel portions are provided, is provided at a separated condensingposition of the pixel portions, the optical system, and the micro lensarray, which is offset from a position at which the images of the pixelportions are focused by the optical system.

Further, it is desirable for the spatial light modulating element to bea DMD (Digital Micro mirror Device), in which micro mirrors are arrangedtwo dimensionally as the pixel portions.

Note that the aforementioned “separated condensing position” refers to aposition, separated from the focusing position of the pixel portions bythe optical system, at which light beams reflected by each of the pixelportions are condensed individually and separated according to the pixelportion by which they were reflected. Alternatively, the “separatedcondensing position” refers to a position at which the light beamsreflected by each of the pixel portions are separated, according to thepixel portion by which they were reflected.

In the first image exposure apparatus of the present invention, each ofthe micro lenses of the micro lens array has different powers in twodirections within a plane perpendicular to the optical axes, in order tocorrect aberrations that occur due to anisotropic distortions of thepixel portions. Therefore, even if the pixel portions of the spatiallight modulating element has anisotropic distortions, the micro lensesof the micro lens array correct astigmatic aberrations caused by thedistortions. Thereby, the beam waist positions in the X and Y directionsof the light beams, which have been condensed by the micro lenses viathe pixel portions, can be matched. Accordingly, the first imageexposure apparatus of the present invention is capable of utilizinglight beams having beam waist positions matched in the X and Ydirections to expose images, thereby enabling obtainment of highlydetailed images.

In addition, the first image exposure apparatus according to the presentinvention provides the micro lens array, for correcting astigmaticaberrations, in the vicinity of the position at which the images of thepixel portions are focused. Therefore, the range of the aforementionedseparated condensing position, at which the light beams reflected byeach of the pixel portions are condensed individually, is wide.

A configuration may be adopted, wherein the first image exposureapparatus of the present invention further comprises the condensingmicro lens array for individually condensing the light beams reflectedby each of the pixel portions, provided at the separated condensingposition. In this case, the beam spot size can be further condensed,which contributes to improvement of the resolution of images exposed bythe image exposure apparatus. In addition, the light beams are alreadycondensed by the micro lens array provided in the vicinity of thefocusing position. Therefore, the beam diameters of the light beams thatenter the condensing micro lens array at the separated condensingposition are smaller than those at the focusing position. Accordingly,eclipsing of the light beams and entrance of the light beams into microlenses adjacent to those that they are intended to enter are prevented,even if the spatial light modulating element and the condensing microlens array are shifted somewhat. Therefore, reductions in the lightutilization efficiency and the extinction ratio, which need to beconsidered when providing the condensing micro lens array, areprevented.

The second image exposure apparatus of the present invention comprisesthe micro lens array provided at the aforementioned separated condensingposition. The beam spots at the separated condensing position aresmaller than those of the images of the pixel portions at the focusingposition, and smaller than the micro lenses of the micro lens array.Accordingly, eclipsing of the light beams and entrance of the lightbeams into micro lenses adjacent to those that they are intended toenter are prevented, even if the spatial light modulating element andthe condensing micro lens array are shifted somewhat. Therefore,reductions in the light utilization efficiency and the extinction ratioare prevented.

In addition, each of the micro lenses of the micro lens array havedifferent powers in two directions within a plane perpendicular to theoptical axes, to correct aberrations caused by the pixel portions havingpowers of different signs in two directions within a plane perpendicularto the optical axes. By adopting this configuration, the beam waistpositions in the X and Y directions of the light beams can be matched,even if astigmatic aberrations occur due to the pixel portions.Accordingly, the second image exposure apparatus of the presentinvention is capable of utilizing light beams having beam waistpositions matched in the X and Y directions to expose images, therebyenabling obtainment of highly detailed images.

The third image exposure apparatus of the present invention comprisesthe micro lens array, provided at the aforementioned separatedcondensing position. The beam spots at the separated condensing positionare smaller than those of the images of the pixel portions at thefocusing position, and smaller than the micro lenses of the micro lensarray. Accordingly, eclipsing of the light beams and entrance of thelight beams into micro lenses adjacent to those that they are intendedto enter are prevented, even if the spatial light modulating element andthe condensing micro lens array are shifted somewhat. Therefore,reductions in the light utilization efficiency and the extinction ratioare prevented.

In addition, each of the micro lenses of the micro lens array havedifferent powers in two directions within a plane perpendicular to theoptical axes, to correct aberrations caused by the pixel portions havingdifferent powers of the same sign in two directions within a planeperpendicular to the optical axes. By adopting this configuration, thebeam waist positions in the X and Y directions of the light beams can bematched, even if astigmatic aberrations occur due to the pixel portions.Accordingly, the second image exposure apparatus of the presentinvention is capable of utilizing condensed light beams having beamwaist positions matched in the X and Y directions to expose images,thereby enabling obtainment of highly detailed images.

A configuration may be adopted, wherein the second and third imageexposure apparatuses of the present invention further comprise thecondensing micro lens array, for individually condensing the light beamswhich have propagated thereto via each of the pixel portions, providedat the aforementioned separated condensing position. In this case, thebeam spot size can be further condensed, which contributes toimprovement of the resolution of images exposed by the image exposureapparatus. In addition, the light beams are already condensed by themicro lens array provided in the vicinity of the focusing position.Therefore, the beam diameters of the light beams that enter thecondensing micro lens array at the separated condensing position aresmaller than those at the focusing position. Accordingly, eclipsing ofthe light beams and entrance of the light beams into micro lensesadjacent to those that they are intended to enter are prevented, even ifthe spatial light modulating element and the condensing microlens arrayare shifted somewhat. Therefore, reductions in the light utilizationefficiency and the extinction ratio, which need to be considered whenproviding the condensing micro lens array, are prevented.

The condensing micro lens array may be provided to be movable in thedirection of the optical axes of the light beams. In this case,adjustments to the focal point of the light beams are facilitated. Thevariance in light utilization efficiency at the separated condensingposition and the vicinity thereof is smaller than that at the focusingposition and the vicinity thereof. Therefore, the variance in lightutilization efficiency can be suppressed to a minimum.

In addition, the aperture array may be provided at the separatedcondensing position, in the first through third image exposureapparatuses of the present invention. In this case, each of theapertures transmits only the light beams which have been condensed viathe corresponding pixel portions. Therefore, stray light can be shutout, and the extinction ratio can be improved.

Note that in the case that gradient index lenses are employed as themicro lenses in the first through third image exposure apparatuses ofthe present invention, the exterior shape can be formed as a parallelplane. In the case that diffraction lenses are employed as the microlenses, the exterior shape can be formed as a parallel plane, whilereducing the thickness in the direction of the optical axes, compared toa case in which refractive lenses are employed. In the case thatcombinations of at least two of refractive lenses, gradient indexlenses, and diffraction lenses are employed, the degree of freedom indesign increases.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view that illustrates the outer appearance of animage exposure apparatus according to a first embodiment of the presentinvention.

FIG. 2 is a perspective view that illustrates the construction of ascanner of the image exposure apparatus according to the firstembodiment of the present invention.

FIG. 3A is a plan view that illustrates exposed regions, which areformed on a photosensitive material.

FIG. 3B is a diagram that illustrates the arrangement of exposure areasexposed by exposure heads.

FIG. 4 is a perspective view that illustrates the schematic constructionof an exposure head of the image exposure apparatus according to thefirst embodiment of the present invention.

FIG. 5 is a schematic sectional view that illustrates the exposure headof the image exposure apparatus according to the first embodiment of thepresent invention.

FIG. 6 is a partial magnified diagram that illustrates the constructionof a digital micro mirror device (DMD).

FIG. 7A is a diagram for explaining the operation of the DMD.

FIG. 7B is a diagram for explaining the operation of the DMD.

FIG. 8A is a plan view that illustrates the scanning trajectories ofexposing beams in the case that the DMD is not inclined.

FIG. 8B is a plan view that illustrates the scanning trajectories of theexposing beams in the case that the DMD is inclined.

FIG. 9A is a perspective view that illustrates the construction of afiber array light source.

FIG. 9B is a front view that illustrates the arrangement of lightemitting points of laser emitting portions of the fiber array lightsource.

FIG. 10 is a diagram that illustrates the configuration of multi modeoptical fibers.

FIG. 11 is a plan view that illustrates the construction of a multiplexlaser light source.

FIG. 12 is a plan view that illustrates the construction of a lasermodule.

FIG. 13 is a side view of the laser module of FIG. 12.

FIG. 14 is a partial front view of the laser module of FIG. 12.

FIG. 15 is a block diagram that illustrates the electrical configurationof the image exposure apparatus according to the first embodiment of thepresent invention.

FIG. 16A is a diagram that illustrates an example of a utilized regionof the DMD.

FIG. 16B is a diagram that illustrates an example of a utilized regionof the DMD.

FIG. 17 is a diagram that illustrates the direction of a deflecting axisof a micro mirror of the DMD.

FIG. 18A is a graph that schematically illustrates the heightdisplacement of a reflective surface of the micro mirror in a planeparallel to an x direction.

FIG. 18B is a graph that schematically illustrates the heightdisplacement of a reflective surface of the micro mirror in a planeparallel to a y direction.

FIG. 19A is a diagram that illustrates how light reflected by the micromirror propagates within a plane parallel to the x direction.

FIG. 19B is a diagram that illustrates how light reflected by the micromirror propagates within a plane parallel to the y direction.

FIG. 20A is a front view of a micro lens array.

FIG. 20B is a side view of the micro lens array.

FIG. 21A is a perspective view of a micro lens of the micro lens array.

FIG. 21B is a view of a cross section of the micro lens parallel to thex direction.

FIG. 21C is a view of a cross section of the micro lens parallel to they direction.

FIG. 22A is a diagram for explaining how the micro lens correctsaberrations.

FIG. 22B is a diagram for explaining how the micro lens correctsaberrations.

FIG. 22C is a diagram for explaining how the micro lens correctsaberrations.

FIG. 23A is a front view of a second example of the micro lens.

FIG. 23B is a side view of the second example of the micro lens.

FIG. 24A is a schematic diagram that illustrates the condensing state bythe micro lens of FIGS. 23A and 23B, in a cross section parallel to thex direction.

FIG. 24B is a schematic diagram that illustrates the condensing state bythe micro lens of FIGS. 23A and 23B, in a cross section parallel to they direction.

FIG. 25A is a schematic diagram that illustrates the condensing state ofa third example of the micro lens in a cross section parallel to the xdirection.

FIG. 25B is a schematic diagram that illustrates the condensing state ofthe third example of the micro lens in a cross section parallel to the ydirection.

FIG. 26A is a front view of a fourth example of the micro lens.

FIG. 26B is a side view of the fourth example of the micro lens.

FIG. 27A is a front view of a fifth example of the micro lens.

FIG. 27B is a side view of the fifth example of the micro lens.

FIG. 28 is a schematic sectional view that illustrates an exposure headof the image exposure apparatus according to a second embodiment of thepresent invention.

FIG. 29 is a schematic sectional view that illustrates an exposure headof the image exposure apparatus according to a third embodiment of thepresent invention.

FIG. 30 is a schematic sectional view that illustrates an exposure headof the image exposure apparatus according to a fourth embodiment of thepresent invention.

FIG. 31 is a schematic sectional view that illustrates an exposure headof the image exposure apparatus according to a fifth embodiment of thepresent invention.

FIG. 32A is a diagram for explaining how the micro lens correctsaberrations.

FIG. 32B is a diagram for explaining how the micro lens correctsaberrations.

FIG. 33A is a diagram for explaining the advantageous effects of theimage exposure apparatus according to the fifth embodiment of thepresent invention.

FIG. 33B is a diagram for explaining the advantageous effects of theimage exposure apparatus according to the fifth embodiment of thepresent invention.

FIG. 34A is a diagram for explaining the advantageous effects of theimage exposure apparatus according to the fifth embodiment of thepresent invention.

FIG. 34B is a diagram for explaining the advantageous effects of theimage exposure apparatus according to the fifth embodiment of thepresent invention.

FIG. 35 is a schematic sectional view that illustrates an exposure headof the image exposure apparatus according to a sixth embodiment of thepresent invention.

FIG. 36 is a schematic sectional view that illustrates an exposure headof the image exposure apparatus according to a seventh embodiment of thepresent invention.

FIG. 37 is a schematic sectional view that illustrates an exposure headof the image exposure apparatus according to an eighth embodiment of thepresent invention.

FIG. 38 is a schematic sectional view that illustrates an exposure headof the image exposure apparatus according to a ninth embodiment of thepresent invention.

FIG. 39A is a schematic diagram that illustrates distortion in thereflective surface of a micro mirror in the x direction.

FIG. 39B is a schematic diagram that illustrates distortion in thereflective surface of a micro mirror in the y direction.

FIG. 40A is a schematic diagram that illustrates how light reflected bythe micro mirror propagates within a plane parallel to the x direction.

FIG. 40B is a schematic diagram that illustrates how light reflected bythe micro mirror propagates within a plane parallel to the y direction.

FIG. 41A is a diagram for explaining how the micro lens correctsaberrations.

FIG. 41B is a diagram for explaining how the micro lens correctsaberrations.

FIG. 42A is a front view of a sixth example of a micro lens.

FIG. 42B is a side view of the sixth example of a micro lens.

FIG. 43A is a schematic diagram that illustrates the condensing state bythe micro lens of FIGS. 42A and 42B, in a cross section parallel to thex direction.

FIG. 43B is a schematic diagram that illustrates the condensing state bythe micro lens of FIGS. 42A and 42B, in a cross section parallel to they direction.

FIG. 44A is a diagram for explaining how the micro lens correctsaberrations.

FIG. 44B is a diagram for explaining how the micro lens correctsaberrations.

FIG. 45 is a schematic sectional view that illustrates an exposure headof the image exposure apparatus according to a tenth embodiment of thepresent invention.

FIG. 46 is a schematic sectional view that illustrates an exposure headof the image exposure apparatus according to an eleventh embodiment ofthe present invention.

FIG. 47 is a schematic sectional view that illustrates an exposure headof the image exposure apparatus according to a twelfth embodiment of thepresent invention.

FIGS. 48A and 48B are diagrams for explaining the problems associatedwith conventional image exposure apparatuses.

FIGS. 49A and 49B are diagrams for explaining the problems associatedwith conventional image exposure apparatuses.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to the attached drawings. First, animage exposure apparatus according to a first embodiment of the presentinvention will be described.

[Configuration of the Image Exposure Apparatus]

As illustrated in FIG. 1, the image exposure apparatus is equipped witha planar moving stage 152, for holding sheets of photosensitive material150 thereon by suction. Amounting base 156 is supported by four legs154. Two guides 158 that extend along the stage movement direction areprovided on the upper surface of the mounting base 156. The stage 152 isprovided such that its longitudinal direction is aligned with the stagemovement direction, and supported by the guides 158 so as to be movablereciprocally thereon. Note that the image exposure apparatus is alsoequipped with a stage driving apparatus 304 (refer to FIG. 15), as a subscanning means for driving the stage 152 along the guides 158.

A C-shaped gate 160 is provided at the central portion of the mountingbase so as to straddle the movement path of the stage 152. The ends ofthe C-shaped gate 160 are fixed to side edges of the mounting base 156.A scanner 162 is provided on a first side of the gate 160, and aplurality (two, for example) of sensors 164 for detecting the leadingand trailing ends of the photosensitive material 150 are provided on asecond side of the gate 160. The scanner 162 and the sensors 164 areindividually mounted on the gate 160, and fixed above the movement pathof the stage 152. Note that the scanner 162 and the sensors 164 areconnected to a controller (not shown) for controlling the operationsthereof.

The scanner 162 is equipped with a plurality (14, for example) ofexposure heads 166, arranged in an approximate matrix having m rows andn columns (3 rows and 5 columns, for example), as illustrated in FIG. 2and FIG. 3B. In this example, four exposure heads 166 are provided inthe third row, due to constraints imposed by the width of thephotosensitive material 150. Note that an individual exposure headarranged in an m^(th) row and an n^(th) column will be denoted as anexposure head 166 _(mn).

An exposure area 168, which is exposed by the exposure heads 166, is arectangular area having its short sides in the sub-scanning direction.Accordingly, band-like exposed regions 170 are formed on thephotosensitive material 150 by each of the exposure heads 166,accompanying the movement of the stage 152. Note that an individualexposure area, exposed by an exposure head arranged in an m^(th) row andan n^(th) column will be denoted as an exposure area 168 _(m, n).

As illustrated in FIG. 3B, each of the rows of the exposure heads 166 isprovided staggered a predetermined interval (a natural number multipleof the long side of the exposure area, 2 times in the presentembodiment) with respect to the other rows. This is to ensure that theband-like exposed regions 170 have no gaps therebetween in the directionperpendicular to the sub scanning direction, as illustrated in FIG. 3A.Therefore, the portion between an exposure area 168 _(1, 1) and 168_(1, 2) of the first row, which cannot be exposed thereby, can beexposed by an exposure area 168 _(2, 1) of the second row and anexposure area 168 _(3, 1) of the third row.

Each of the exposure heads 166 _(1, 1) through 168 _(m, n) are equippedwith a DMD 50 (Digital Micro mirror Device) by Texas Instruments (U.S.),for modulating light beams incident thereon according to each pixel ofimage data. The DMD's 50 are connected to a controller 302 to bedescribed later (refer to FIG. 15), comprising a data processing sectionand a mirror drive control section. The data processing section of thecontroller 302 generates control signals for controlling the drive ofeach micro mirror of the DMD 50 within a region that should becontrolled for each exposure head 166, based on input image data. Notethat the “region that should be controlled” will be described later. Themirror drive control section controls the angle of a reflective surfaceof each micro mirror of the DMD 50 for each exposure head 166, accordingto the control signals generated by the data processing section. Notethat control of the angle of the reflective surface will be describedlater.

A fiber array light source 66; an optical system 67; and a mirror 69 areprovided in this order, at the light incident side of the DMD 50. Thefiber array light source 66 comprises a laser emitting section,constituted by a plurality of optical fibers having their light emittingends (light emitting points) aligned in a direction corresponding to thelongitudinal direction of the exposure area 168. The optical system 67corrects laser beams emitted from the fiber array light source 66 tocondense them onto the DMD 50. The mirror 69 reflects the laser beams,which have passed through the optical system 67, toward the DMD 50. Notethat the optical system 67 is schematically illustrated in FIG. 4.

As illustrated in detail in FIG. 5, the optical system 67 comprises: acondensing lens 71, for condensing the laser beams B emitted from thefiber array light source 66 as illuminating light; a rod-like opticalintegrator 72 (hereinafter, referred to simply as “rod integrator 72”),which is inserted into the optical path of the light which has passedthrough the condensing lens 71; and a collimating lens 74, provideddownstream from the rod integrator 72, that is, toward the side of themirror 69. The condensing lens 71, the rod integrator 72 and thecollimating lens 74 cause the laser beams emitted from the fiber arraylight source to enter the DMD 50 as a light beam which is close tocollimated light and which has uniform beam intensity across its crosssection. The shape and the operation of the rod integrator 72 will bedescribed in detail later.

The laser beam B emitted through the optical system 67 is reflected bythe mirror 69, and is irradiated onto the DMD 50 via a TIR (TotalInternal Reflection) prism 70. Note that the TIR prism 70 is omittedfrom FIG. 4.

A focusing optical system 51, for focusing the laser beam B reflected bythe DMD 50 onto the photosensitive material 150, is provided on thelight reflecting side of the DMD 50. The focusing optical system 51 isschematically illustrated in FIG. 4, but as illustrated in detail inFIG. 5, the focusing optical system 51 comprises: a first focusingoptical system constituted by lens systems 52 and 54; a second focusingoptical system constituted by lens systems 57 and 58; a micro lens array55; and an aperture array 59. The micro lens array 55 and the aperturearray 59 are provided between the first focusing optical system and thesecond focusing optical system.

The micro lens array 55 is constituted by a great number of micro lenses55 a, which are arranged two dimensionally, corresponding to each pixelof the DMD 50. In the present embodiment, only 1024×256 columns out of1024×768 columns of micro mirrors of the DMD 50 are driven, as will bedescribed later. Therefore, 1024×256 columns of micro lenses 55 a areprovided, corresponding thereto. The arrangement pitch of the microlenses 55 a is 41 μm in both the vertical and horizontal directions. Themicro lenses 55 a are formed by optical glass BK7, and have focaldistances of 0.19 mm and NA's (Numerical Apertures) of 0.11, forexample. Note that the shapes of the micro lenses 55 a will be describedin detail later. The beam diameter of each laser beams B at the positionof each micro lens 55 a is 41 μm.

The aperture array 59 has a great number of apertures 59 a formedtherethrough, corresponding to the micro lenses 55 a of the micro lensarray 55. In the present embodiment, the diameter of the apertures 59 ais 10 μm.

The first focusing optical system magnifies the images that propagatethereto from the DMD 50 by 3× and focuses the images on the micro lensarray 55. The second focusing optical system magnifies the images thathave passed through the micro lens array 55 by 1.6×, and focuses theimages onto the photosensitive material 150. Accordingly, the imagesfrom the DMD 50 are magnified at 4.8× magnification and projected ontothe photosensitive material 150.

Note that in the present embodiment, a prism pair 73 is provided betweenthe second focusing optical system and the photosensitive material 150.The focus of the image on the photosensitive material 150 is adjustable,by moving the prism pair 73 in the vertical direction in FIG. 5. Notethat in FIG. 5, the photosensitive material 150 is conveyed in thedirection of arrow F to perform sub-scanning.

The DMD 50 is a mirror device having a great number (1024×768, forexample) of micro mirrors 62, each of which constitutes a pixel,arranged in a matrix on an SRAM cell 60 (memory cell). A micro mirror 62supported by a support column is provided at the uppermost part of eachpixel, and a material having high reflectivity, such as aluminum, isdeposited on the surface of the micro mirror 62 by vapor deposition.Note that the reflectivity of the micro mirrors 62 is 90% or greater,and that the arrangement pitch of the micro mirrors 62 is 13.7 μm inboth the vertical and horizontal directions. In addition, the CMOS SRAMcell 60 of a silicon gate, which is manufactured in a normalsemiconductor memory manufacturing line, is provided beneath the micromirrors 62, via the support column, which includes a hinge and a yoke.The DMD 50 is of a monolithic structure.

When digital signals are written into the SRAM cell 60 of the DMD 50,the micro mirrors 62 which are supported by the support columns aretilted within a range of ±α degrees (±12 degrees, for example) withrespect to the substrate on which the DMD 50 is provided, with thediagonal line as the center of rotation. FIG. 7A illustrates a state inwhich a micro mirror 62 is tilted ±α degrees in an ON state, and FIG. 7Billustrates a state in which a micro mirror 62 is tilted −α degrees inan OFF state. Accordingly, laser light beams incident on the DMD 50 arereflected toward the direction of inclination of each micro mirror 62,by controlling the tilt of each micro mirror 62 that corresponds to apixel of the DMD 50 according to image signals, as illustrated in FIG.6.

Note that FIG. 6 illustrates a magnified portion of a DMD 50 in whichthe micro mirrors 62 are controlled to be tilted at +α degrees and at −αdegrees. The ON/OFF operation of each micro mirror 62 is performed bythe controller 302, which is connected to the DMD 50. In addition, alight absorbing material (not shown) is provided in the direction towardwhich laser beams B reflected by micro mirrors 62 in the OFF state arereflected. The micro mirrors 62 of the present embodiment havedistortions in their reflective surfaces. However, the distortions areomitted from FIGS. 6, 7A, and 7B.

It is preferable for the DMD 50 to be provided such that its short sideis inclined at a slight predetermined angle (0.1° to 5°, for example)with respect to the sub-scanning direction. FIG. 8A illustrates scanningtrajectories of reflected light images 53 (exposing beams) of each micromirror in the case that the DMD 50 is not inclined, and FIG. 8Billustrates the scanning trajectories of the exposing beams 53 in thecase that the DMD 50 is inclined.

A great number (756, for example) of columns of rows of a great number(1024, for example) of micro mirrors aligned in the longitudinaldirection, are provided in the lateral direction of the DMD 50. Asillustrated in FIG. 8B, by inclining the DMD 50, the pitch P₂ of thescanning trajectories (scanning lines) of the exposure beams 53 becomenarrower than the pitch P₁ of the scanning lines in the case that theDMD 50 is not inclined. Therefore, the resolution of the image can begreatly improved. Meanwhile, because the angle of inclination of the DMD50 is slight, the scanning width W₂ in the case that the DMD 50 isinclined and the scanning width W₁ in the case that the DMD is notinclined are substantially the same.

In addition, the same scanning lines are repeatedly exposed (multipleexposure) by different micro mirror columns. By performing multipleexposure in this manner, it becomes possible to finely control exposurepositions with respect to alignment marks, and to realize highlydetailed exposure. Seams among the plurality of exposure heads, whichare aligned in the main scanning direction, can be rendered virtuallyseamless by finely controlling the exposure positions.

Note that the micro mirror columns may be shifted by predeterminedintervals in the direction perpendicular to the sub-scanning directionto be in a staggered formation instead of inclining the DMD 50, toachieve the same effect.

As illustrated in FIG. 9A, the fiber array light source 66 is equippedwith a plurality (14, for example) of laser modules 64. An end of amulti mode optical fiber 30 is coupled to each laser module 64. Anoptical fiber 31, having the same core diameter as the multi modeoptical fiber 30 and a cladding diameter smaller than that of the multimode optical fiber 30, is coupled to the other end of each multi modeoptical fiber 30. As illustrated in detail in FIG. 9B, the opticalfibers 31 are arranged such that seven ends of the optical fibers 30opposite the end at which they are coupled to the multi mode opticalfibers are aligned along the main scanning direction perpendicular tothe sub scanning direction. Two rows of the seven optical fibers 31constitute a laser emitting section 68.

As illustrated in FIG. 9B, the laser emitting section 68, constituted bythe ends of the optical fibers 31, is fixed by being sandwiched betweentwo support plates 65, which have flat surfaces. It is desirable for atransparent protective plate, such as that made of glass, to be placedat the light emitting end surfaces of the optical fibers 31. The lightemitting end surfaces of the optical fibers 31 are likely to collectdust due to their high optical density and therefore likely todeteriorate. However, by placing the protective plate as describedabove, adhesion of dust to the end surfaces can be prevented, anddeterioration can be slowed.

In the present embodiment, the optical fiber 31 having a small claddingdiameter and a length of approximately 1 to 30 cm is coaxially coupledto the light emitting end of the multi mode optical fiber 30 having alarge cladding diameter, as illustrated in FIG. 10. Each pair of theoptical fibers 30 and 31 are coupled by fusing the light incident endsurface of the optical fiber 31 with the light emitting end surface ofthe multi mode optical fiber 30 such that the core axes thereof arematched. As described above, the diameter of the core 31 a of theoptical fiber 31 is the same as the diameter of the core 30 a of themulti mode optical fiber 30.

Step index type optical fibers, graded index type optical fibers, orcombined type optical fibers may be employed as the multi mode opticalfibers 30 and the optical fibers 31. Step index type optical fibersproduced by Mitsubishi Wire Industries KK may be employed, for example.In the present embodiment, the multi mode optical fibers 30 and theoptical fibers 31 are step index type optical fibers. The multi modeoptical fiber 30 has a cladding diameter of 125 μm, a core diameter of50 μm, and an NA of 0.2. The optical fiber 30 has a cladding diameter of60 μm, a core diameter of 50 μm, and an NA of 0.2. The transmissivity ofthe coating at the light incident end surface of the multi mode opticalfiber 30 is 99.5% or greater.

The cladding diameter of the optical fiber 31 is not limited to being 60μm. The cladding diameters of many optical fibers, which are utilized inconventional fiber light sources, are 125 μm. However, the focal depthbecomes deeper as the cladding diameter decreases. Therefore, it ispreferable for the cladding layer of a multi mode optical fiber to be 80μm or less, and more preferably, 60 μm or less. Meanwhile, in the caseof a single mode optical fiber, it is necessary for the core diameter tobe at least 3 to 4 μm. Therefore, it is preferable for the claddingdiameter of the optical fiber 31 to be 10 μm or greater. It ispreferable for the core diameter of the multi mode optical fiber 30 andthe core diameter of the optical fiber 31 to be matched, from theviewpoint of coupling efficiency.

Each of the laser modules 64 is constituted by the multiplex laser lightsource (fiber light source) illustrated in FIG. 11. The multiplex laserlight source comprises: a heat block 10; a plurality (seven, forexample) GaN type semiconductor laser chips LD1, LD2, LD3, LD4, LD5,LD6, and LD7, which are aligned and fixed on the heat block 10;collimating lenses 11, 12, 13, 14, 15, 16, and 17, providedcorresponding to each of the GaN type semiconductor lasers LD1 throughLD7; a single condensing lens 20; and a single multi mode fiber 30. TheGaN type semiconductor laser chips may be transverse multi mode laserchips or single mode laser chips. Note that the number of semiconductorlasers is not limited to 7, and any number of semiconductor lasers maybe employed. In addition, a collimating lens array, in which thecollimating lenses 11 through 17 are integrated, may be employed insteadof the collimating lenses 11 through 17.

All of the GaN type semiconductor lasers LD1 through LD7 have the sameoscillating wavelength (405 nm, for example), and the same maximumoutput (in the case of multi mode lasers, approximately 100 mW, and inthe case of single mode lasers, approximately 50 mW). Note that the GaNsemiconductors may have any oscillating wavelengths other than 405 nm,within a wavelength range of 350 nm to 450 nm.

As illustrated in FIGS. 12 and 13, the multiplex laser light source ishoused within a box-shaped package 40 having an open top, along withother optical components. The package 40 is equipped with a package lid41, formed to seal the open top. The package 40 is deaerated, sealinggas is introduced, and the package lid 41 is placed on the package.Thereby, the multiplex laser light source is hermetically sealed withinthe closed space (sealed space) of the package 40.

A base plate 42 is fixed on the bottom surface of the package 40. Theheat block 10, a condensing lens holder 45 for holding the condensinglens 20, and a fiber holder 46 for holding the light incident end of themulti mode optical fiber 30 are mounted on the base plate 42. The lightemitting end of the multi mode optical fiber 30 is pulled out to theexterior of the package 40 through an opening formed in a wall thereof.

A collimating lens holder 44 is mounted on a side surface of the heatblock 10, and the collimating lenses 11 through 17 are held thereby. Anopening is formed in a side wall of the package 40, and wires 47 forsupplying drive current to the GaN type semiconductor lasers LD1 throughLD7 are pulled out toward the exterior of the package 40 therethrough.

Note that in FIG. 13, only the GaN type semiconductor laser LD7 and thecollimating lens 17 are labeled with reference numbers, in order toavoid complexity in the drawing.

FIG. 14 is a front view of the mounting portions of the collimatinglenses 11 through 17. Each of the collimating lenses 11 through 17 isformed to be of an elongate shape, obtained by cutting out a region thatincludes the optical axis of a circular lens having an asphericalsurface. The elongate collimating lenses may be formed by molding resinor optical glass, for example. The collimating lenses 11 through 17 aredensely provided and such that their longitudinal directions areperpendicular to the arrangement direction of the light emitting pointsof the GaN type semiconductor lasers LD1 through LD7 (the horizontaldirection in FIG. 14).

The GaN type semiconductor lasers LD1 through LD7 comprise active layershaving light emitting widths of 2 μm. Laser beams B1 through B7 havingbeam spread angles of 10 degrees and 30 degrees in the directionparallel to the active layer and the direction perpendicular to theactive layer, respectively, are emitted from the GaN type semiconductorlasers LD1 through LD7. The GaN type semiconductor lasers LD1 throughLD7 are provided such that the light emitting points thereof are alignedin a direction parallel to the active layers thereof.

Accordingly, the laser beams B1 through B7 are emitted from each of thelight emitting points such that they enter the collimating lenses 11through 17 in a state in which the directions that their beam spreadangles are greater match the lengthwise directions of the collimatinglenses 11 through 17, and in which the directions that their beam spreadangles are smaller match the width directions of the collimating lenses11 through 17. The widths and lengths of each of the collimating lenses11 through 17 are 1.1 mm and 4.6 mm, respectively. The beam diameters ofthe laser beams B1 through B7 in the horizontal direction and thevertical direction are 0.9 mm and 2.6 mm, respectively. The collimatinglenses 11 through 17 have focal distances f₁ of 3 mm, numericalapertures NA of 0.6, and are arranged at a pitch of 1.25 mm.

The condensing lens 20 is obtained by cutting out an elongate regionthat includes the optical axis of a circular lens having an asphericalsurface at parallel planes. The condensing lens 20 is formed such thatit is long in the arrangement direction of the collimating lenses 11through 17, that is, the horizontal direction, and short in thedirection perpendicular to the arrangement direction. The condensinglens 20 has a focal distance f₂ of 23 mm, and a numerical aperture NA of0.2. The condensing lens 20 may also be formed by molding resin oroptical glass, for example.

Next, the electrical configuration of the image exposure apparatus ofthe present embodiment will be described with reference to FIG. 15. Asillustrated in FIG. 15, a total control section 300 is connected to amodulating circuit 301, which in turn is connected to the controller 302for controlling the DMD's 50. The total control section 300 is alsoconnected to a LD drive circuit 303, for driving the laser modules 64.Further, the total control section 300 is connected to the stage drivingapparatus 304, for driving the stage 152.

[Operation of the Image Exposure Apparatus]

Next, the operation of the image exposure apparatus described above willbe described. The laser beams B1 through B7 are emitted by each of theGaN semiconductor lasers LD1 through LD7 (refer to FIG. 11) thatconstitute the multiplex laser light source of the fiber array lightsource 66 in a diffuse state. The laser beams B1 through B7 arecollimated by the collimating lens corresponding thereto, from among thecollimating lenses 11 through 17. The collimated laser beams B5 throughB7 are condensed by the condensing lens 20, and are converged onto thelight incident surface of the core 30 a of the multi mode optical finer30.

In the present embodiment, the collimating lenses 11 through 17 and thecondensing lens 20 constitute a condensing optical system, and thecondensing optical system and the multi mode optical fiber 30 constitutea multiplex optical system. That is, the laser beams B5 through B7,which have been condensed by the condensing lens 20 enter the core 30 aof the multi mode optical fiber 30, are multiplexed into a single laserbeam B, and emitted from the optical fiber 31, which is coupled to thelight emitting end of the multi mode optical fiber 30.

The coupling efficiency of the laser beams B1 through B7 with respect tothe multi mode optical fiber 30 is 0.9 in each of the laser modules. Inthe case that the output of each of the GaN type semiconductor lasersLD1 through LD7 is 50 mW, a multiplexed laser beam B having an output of315 mW (50 mW×0.9×7) can be obtained from each of the optical fibers 31which are provided in the array. Accordingly, a laser beam B having anoutput of 4.4 W (0.315 W×14) can be obtained from the 14 combinedoptical fibers 31.

During image exposure, image data corresponding to an exposure patternis input to the controller 302 of the DMD's 50 from the modulatingcircuit 301. The image data is temporarily stored in a frame memory ofthe controller 302. The image data represents the density of each pixelthat constitutes an image as binary data (dot to be recorded/dot not tobe recorded).

The stage 152, on the surface of which the photosensitive material 150is fixed by suction, is conveyed along the guides 158 from the upstreamside to the downstream side of the gate 160 by the stage drivingapparatus 304 illustrated in FIG. 15. When the stage 152 passes underthe gate 160, the leading edge of the photosensitive material isdetected by the sensors 164, which are mounted on the gate 160. Then,the image data recorded in the frame memory is sequentially read out aplurality of lines at a time. Control signals are generated by thesignal processing section for each exposure head 166, based on the readout image data. Thereafter, the mirror driving control section controlsthe ON/OFF states of each micro mirror of the DMD's 50 of each exposurehead, based on the generated control signals. Note that in the presentembodiment, the size of each micro mirror that corresponds to a singlepixel is 14 μm×14 μm.

When the laser beam B is irradiated onto the DMD's 50 from the fiberarray light source 66, laser beams which are reflected by micro mirrorsin the ON state are focused on the photosensitive material 150 by thelens systems 54 and 58. The laser beams emitted from the fiber arraylight source 66 are turned ON/OFF for each pixel, and the photosensitivematerial 150 is exposed in pixel units (exposure areas 168)substantially equal to the number of pixels of the DMD's 50 in thismanner. The photosensitive material 150 is conveyed with the stage 152at the constant speed. Sub-scanning is performed in the directionopposite the stage moving direction by the scanner 162, and band-shapedexposed regions 170 are formed on the photosensitive material 150 byeach exposure head 166.

Note that in the present embodiment, 768 columns of micro mirror rowshaving 1024 micro mirrors therein are provided on each DMD 50 in the subscanning direction, as illustrated in FIGS. 16A and 16B. However, only aportion of the micro mirror columns (256 columns of 1024 micro mirrors,for example) is driven by the controller 302.

In this case, the micro mirror columns situated at the central portionof the DMD 50 may be utilized, as illustrated in FIG. 16A.Alternatively, the micro mirror columns situated at the edge of the DMD50 may be utilized, as illustrated in FIG. 16B. In addition, the micromirror columns to be utilized may be changed as appropriate, in casesthat defects occur in a portion of the micro mirrors and the like.

The data processing speed of the DMD's 50 is limited, and the modulationspeed for each line is determined proportionate to the number ofutilized pixels. Therefore, the modulation speed is increased byutilizing only a portion of the micro mirror columns. Meanwhile, in thecase that an exposure method is adopted in which the exposure heads arecontinuously moved with respect to the exposure surface, it is notnecessary to utilize all of the pixels in the sub scanning direction.

When sub scanning of the photosensitive material 150 by the scanner 162is completed and the trailing edge of the photosensitive material 150 isdetected by the sensors 162, the stage 152 is returned to its startingpoint at the most upstream side of the gate 160 along the guides 152 bythe stage driving apparatus 304. Then, the stage 152 is moved from theupstream side to the downstream side of the gate 160 at the constantspeed again.

[Details of the Optical Systems of the Image Exposure Apparatus]

Next, an illuminating optical system for irradiating the laser beam Bonto the DMD's 50, comprising: the fiber array 66, the condensing lens71, the rod integrator 72, the collimating lens 74, the mirror 69, andthe TIR prism 70 illustrated in FIG. 5 will be described. The rodintegrator 72 is a light transmissive rod, formed as a square column,for example. The laser beam B propagates through the interior of the rodintegrator 72 while being totally reflected therein, and the intensitydistribution within the cross section of the laser beam B isuniformized. Note that an anti-reflective film is coated on the lightincident surface and the light emitting surface of the rod integrator72, to increase the transmissivity thereof. By uniformizing theintensity distribution within the cross section of the laser beam B inthis manner, unevenness in the intensity of the illuminating light canbe eliminated, and highly detailed images can be exposed on thephotosensitive material 150.

FIG. 17 illustrates the direction of a deflecting axis, which is thecentral axis about which a micro mirror 62 of the DMD 50 rotates. In thepresent embodiment, one of the diagonals of the reflective surface ofthe micro mirror 62 is the direction of the deflecting axis. Thisdirection is designated as a y direction, and the other diagonal isdesignated as an x direction. That is, the x direction and the ydirection are two different directions within a plane perpendicular toan optical axis O, and the two different directions are perpendicular inthe present embodiment.

FIG. 18A and FIG. 18B are graphs that schematically illustrate theheight displacement of the reflective surface of the micro mirror 62 inplanes parallel to the x direction and the y direction, respectively. InFIG. 18A and FIG. 18B, the horizontal axes of the graphs representdistances from the center of the reflective surface in the respectivedirections, and the vertical axes represent displacement in thedirection of the optical axis. As illustrated in FIG. 18A and FIG. 18B,the reflective surface of the micro mirror 62 is a curved surface havinga concave shape in the x direction and a convex shape in the ydirection. That is, the reflective surface is a rotationallyasymmetrical curved surface, and has an anisotropic distortion. Due tothis shape, the micro mirror 62 is of a rotationally asymmetricalstructure that has powers of different signs in the x direction and they direction.

If collimated light is irradiated onto the micro mirror 62 having thepowers of different signs as described above, the reflected light willbe convergent in the x direction and divergent in the y direction. FIG.19A and FIG. 19B are diagrams that illustrate how light reflected by theaforementioned micro mirror 62 propagates through the lens systems 52and 54 that constitute the first focusing system, within planes parallelto the x direction and the y direction, respectively.

Note that the lens systems 52 and 54 have rotationally symmetricalpowers with respect to the optical axis. The TIR prism 70 and the microlens array 55 are omitted from FIG. 19A and FIG. 19B. Three adjacentmicro mirrors 62 are illustrated in FIG. 19A and FIG. 19B. The imagesborne by the light reflected by each of the micro mirrors 62 are denotedby the curved arrows, and the light beams reflected by the center andthe edges of the central micro mirror 62 are denoted by solid lines. Inaddition, the manner in which the beam diameters of the beams reflectedby the three micro mirrors 62 change as the beams propagate downstreamfrom the lens system 54 is denoted by the ovals illustrated by brokenlines in FIG. 19A and FIG. 19B.

In the case that light that converges in the x direction and diverges inthe y direction as described above is condensed by a normal lens, whichhas a power rotationally symmetrical with respect to the optical axis,the position in the direction of the optical axis at which the beamdiameter is minimal (beam waist position) is different in the xdirection and the y direction. That is, an astigmatic aberration occurs,which becomes an obstacle to obtaining highly detailed images.

In order to prevent the aforementioned problem, the micro lenses 55 a ofthe micro lens array 55 of the image exposure apparatus according to thepresent embodiment are of shapes different from conventional microlenses. Hereinafter, this point will be described in detail.

FIG. 20A and FIG. 20B are a front view and a side view of the entiremicro lens array 55, respectively. The dimensions of the micro lensarray 55 are also illustrated in these figures, in units of mm. In thepresent embodiment, 256 columns of 1024 micro mirrors 62 of the DMD 50are driven, as described previously with reference to FIG. 16. The microlens array 55 comprises 256 columns of horizontal rows each including1024 micro lenses 55 a, corresponding to the micro mirrors 62. Note thatin FIG. 20A, the horizontal direction, in which the rows of micro lenses55 a extend, is denoted as j, and the vertical direction is denoted ask.

Each micro lens 55 a has different powers in the x direction and the ydirection, in order to correct the aforementioned anisotropic distortionof the reflective surface of the micro mirrors 62. That is, each microlens 55 a has a power which is rotationally asymmetric with respect tothe optical axis. More specifically, each micro lens 55 a in the presentembodiment is a cylindrical lens having a power of 0 in the x direction,and a power of a positive value in the y direction. The value of thepower in the y direction is determined such that the difference in beamwaist position (astigmatic difference) in the x direction and the ydirection after the laser beam passes through the lens systems 52 and 54and the micro lenses 55 a approximates 0, taking the curvature of thereflective surface of the micro mirror 62 into consideration.

FIG. 21A is a perspective view of an example of such a micro lens 55 a.The micro lens 55 a has a square bottom surface having diagonals in thex direction and the y direction, and a curved upper surface. Asillustrated in FIG. 21B, the micro lens 55 a has a rectangular crosssection parallel to the x direction that passes through the opticalaxis. As illustrated in FIG. 21C, the micro lens 55 a has aprotrusion-shaped cross section, which has a linear bottom and anarcuate top, is parallel to the y direction, and passes through theoptical axis.

The manner in which aberrations caused by the distortion in thereflective surfaces of the micro mirrors 62 is corrected by the microlenses 55 a will be described in greater detail. FIGS. 22A and 22B areschematic diagrams that illustrate the manner in which the lightreflected by the micro mirrors 62 are corrected within cross sectionsthat pass through the optical axis and are parallel to the x directionand the y direction, respectively. The micro lens array 55 is providedin the vicinity of a focusing position, at which the images of the micromirrors 62 are focused by the first focusing optical system.

Note that the TIR prism 70 is omitted from FIGS. 22A and 22B. Threeadjacent micro mirrors 62 are illustrated in FIGS. 22A and 22B, and thelight beams reflected by the center and the edges of the central micromirror 62 are denoted by solid lines. In addition, the manner in whichthe beam diameters of the beams reflected by the three micro mirrors 62change as the beams propagate downstream from the lens system 54 isdenoted by the ovals illustrated by broken lines.

As illustrated in FIG. 22A, the light, which is reflected by the micromirror 62 having the concave shape in the x direction, becomesconvergent light, and enters the micro lens 55 a after passing throughthe lens systems 52 and 54. As described previously, the power of themicro lens 55 a in the x direction is 0. Therefore, the light thatenters the micro lens 55 a propagates without changing its angle withrespect to the optical axis in the x direction, and the beam diameterthereof becomes minimal at its beam waist position.

Meanwhile, as illustrated in FIG. 22B, the light, which is reflected bythe micro mirror having the convex shape in the y direction, becomesdivergent light, and enters the micro lens 55 a after passing throughthe lens systems 52 and 54. As described previously, the micro lens 55 ahas a positive power in the y-direction. Therefore, the light thatenters the micro lens 55 a is condensed in the y direction, and the beamdiameter thereof becomes minimal at the same position as theaforementioned beam waist position of the x direction.

As described above, the micro lens 55 a is configured to have differentpowers in the x direction and the y direction, corresponding to theanisotropic shape of the reflective surface of the micro mirror.Thereby, astigmatic aberrations can be corrected, and the crosssectional shape of the beam can be prevented from becoming oval.Accordingly, the beam waist positions in the x direction and the ydirection are matched, the cross sectional shape of the beam can beshaped, and a condensed beam can be utilized to form images. Therefore,obtainment of highly detailed images becomes possible.

In the above description, a case has been described in which thereflective surfaces of the micro mirrors 62 are concave in the xdirection and convex in the y direction. It is also possible to correctastigmatic aberrations caused by the reflective surfaces of the micromirrors 62, in the case that the reflective surfaces are planar in oneof the x direction and the y direction, and concave or convex in theother. Next, these cases will be described.

First, a case in which a DMD 250 comprising a plurality of micro mirrors262, of which the reflective surfaces are concave in the x direction andplanar in the y direction, is employed to form images will be described.For the sake of simplicity, the concave shape of the micro mirrors 262in the x direction will be the same as the concave shape of the micromirrors 62 in the x direction.

In this case, a micro lens array 55, comprising a plurality of microlenses 55 a′ is employed. Each micro lens 55 a′ is a cylindrical lenshaving a power of 0 in the x direction, and a power of a positive valuesmaller than that of the aforementioned micro lens 55 a in the ydirection. That is, the micro lens 55 a′ has a greater radius ofcurvature in the y direction than the micro lens 55 a. The value of thepower in the y direction of the micro lens 55 a′ is determined such thatthe difference in beam waist position (astigmatic difference) in the xdirection and the y direction after the laser beam passes through thelens systems 52 and 54 and the micro lenses 55 a approximates 0, takingthe curvature of the reflective surface of the micro mirror 62 intoconsideration.

The manner in which aberrations caused by the distortion in thereflective surfaces of the micro mirrors 262 are corrected by the microlenses 55 a′ will be described with reference to FIGS. 22A and 22C. FIG.22C is a schematic diagram that illustrates the manner in which thelight reflected by the micro mirrors 262 is corrected within crosssections that pass through the optical axis and are parallel to the ydirection. The format of FIG. 22C is the same as those of FIGS. 22A and22B. In this case also, the micro lens array 255 is provided in thevicinity of a focusing position, at which the images of the micromirrors 262 are focused by the first focusing optical system.

With regard to the x direction, the operation of the micro lens 55 a′ isthe same as that of the micro lens 55 a described with reference to FIG.22A. Therefore, the beam diameter of the light in the x directionbecomes minimal at its beam waist position.

Meanwhile, as illustrated in FIG. 22C, the light, which is reflected bythe micro mirror having the planar shape in the y direction, enters themicro lens 55 a′ after passing through the lens systems 52 and 54 ascollimated light. As described previously, the micro lens 55 a′ has apositive power in the y direction. Therefore, the light that enters themicro lens 55 a′ is condensed in the y direction, and the beam diameterthereof becomes minimal at the same position as the aforementioned beamwaist position of the x direction.

In this manner, astigmatic aberrations can be corrected even in cases inwhich the reflective surfaces of the micro mirrors have a concave shapeand a planar shape in different directions within a plane perpendicularto the optical axis, by employing micro lenses corresponding to theshape of the reflective surfaces. Accordingly, similar advantageouseffects can be obtained as in the previously described case.

Note that the cross sectional shape of the micro lenses 55 a and 55 a′in the y direction is not limited to the flat bottomed protrusionillustrated in FIG. 21C, and may be a meniscus shape. In addition, thepower of the micro lenses in the direction that the reflective surfacesof the micro mirrors are concave is 0 in the present embodiment.However, the present invention is not limited to this configuration. Themicro lenses may have a positive or negative power in the direction thatthe reflective surfaces of the micro mirrors are concave, as long as thelight becomes convergent after passing through the micro lenses andastigmatic aberrations caused by the micro mirrors can be corrected.

Next, a case will be described in which the reflective surfaces of themicro mirrors are planar in the x direction and convex in the ydirection will be described. In this case, micro lenses having positivepowers in both the x direction and the y direction, with the power inthe x direction being smaller than the power in the y direction, areemployed instead of the cylindrical micro lenses 55 a and 55 a′. A lensconfigured to have cross sectional shapes equal to spherical lenseshaving different radii of curvatures in directions parallel to the xdirection and the y direction is an example of such a micro lens.

The values of the power in the x direction and the y direction of themicro lenses are determined such that the difference in beam waistposition (astigmatic difference) in the x direction and the y directionafter the laser beam passes through the lens systems 52 and 54 and themicro lenses approximates 0, taking the curvature of the reflectivesurface of the micro mirrors into consideration.

In this case, with regard to the x direction, the operation of the microlenses is the same as that of the micro lenses 55 a′ described withreference to FIG. 22C. In addition, with regard to the y direction, theoperation of the micro lenses is the same as that of the micro lenses 55a described with reference to FIG. 22B. Accordingly, the beam waistpositions in the x direction and the y direction can be matched.

In this manner, astigmatic aberrations can be corrected even in cases inwhich the reflective surfaces of the micro mirrors have a planar shapeand a convex shape in different directions within a plane perpendicularto the optical axis, by employing micro lenses corresponding to theshape and curvature of the reflective surfaces. Accordingly, similaradvantageous effects can be obtained as in the previously describedcases.

As described above, even if the reflective surfaces of the micro mirrorshave different shapes in the x direction and the y direction, astigmaticaberrations caused by the micro mirrors can be corrected by setting thepowers of the micro lenses to be different in the x direction and the ydirection. Accordingly, highly detailed images can be obtained.

Note that in the above description, the curved shape of the micro lensesis spherical. However, the present invention is not limited to thisconfiguration, and higher order (quartic, sextic, . . . ) asphericalshapes may be adopted.

In the embodiments described above, each of the micro lenses thatconstitute the micro lens arrays are refractive lenses. Similaradvantageous effects may be obtained by employing gradient index lensesinstead of the refractive lenses. FIG. 23A and FIG. 23B illustrate amicro lens 155 a as an example of such a gradient index lens, whereinFIG. 23A is a front view, and FIG. 23B is a side view. As illustrated inFIG. 23A and FIG. 23B, the micro lens 155 a is of a parallel plateshape. Note that the x and y directions in FIG. 23A are those asdescribed previously.

FIG. 24A and FIG. 24B schematically illustrate the states of the laserbeam B when it passes through the micro lens 155 a in cross sectionsparallel to the x direction and the y direction, respectively. The microlens 155 a has a uniform refractive index distribution in the xdirection, and a refractive index distribution that becomes greatertoward the exterior from the optical axis O in the y direction. Thebroken lines within the micro lens 155 a illustrated in FIG. 24B denotepositions at which the refractive index changes at predetermined pitchesfrom the optical axis O.

As illustrated in FIG. 24A and FIG. 24B, if the cross sections parallelto the x direction and parallel to the y direction are compared, thecollimated light that enters the micro lens 155 a exits as collimatedlight in the cross section parallel to the x direction, while the lightthat enters the micro lens 155 a exits as convergent light in the crosssection parallel to the y direction. The same advantageous effects asthose obtained by employing the micro lens array constituted by theaforementioned micro lenses 55 a and 55 a′ can be obtained by a microlens array constituted by the gradient index lenses.

As a further alternative, micro lenses 255 a, which have refractiveindex distributions is both the x direction and the y direction, whilethe rate of change in refractive index is smaller and the focal distanceis longer in the x direction than in the y direction, may be employed.FIG. 25A and FIG. 25B schematically illustrate the condensing states ofthe laser beam B by the micro lens 255 a in cross sections parallel tothe x direction and the y direction, respectively. The micro lens 255 ahas a refractive index distribution that becomes greater toward theexterior from the optical axis O. The broken lines within the micro lens255 a illustrated in FIG. 25A and FIG. 25B denote positions at which therefractive index changes at predetermined pitches from the optical axisO.

As illustrated in FIG. 25A and FIG. 25B, if the cross sections parallelto the x direction and parallel to the y direction are compared, therate of change of the refractive index is greater in the y direction ofthe micro lens 255 a, and the focal distance is shorter. The sameadvantageous effects as those obtained by employing the micro lens arrayconstituted by the aforementioned micro lenses that have positive powersin both the x direction and the y direction, with a smaller power in thex direction, can be obtained by a micro lens array constituted by thegradient index lenses 255 a.

Further, diffraction lenses may be employed instead of theaforementioned refractive lenses and the gradient index lenses. FIG. 26Aand FIG. 26B illustrate a micro lens 355 a, as an example of such adiffraction lens. FIGS. 26A and 26B are front and side views of themicro lens 355 a, respectively. As illustrated in FIG. 26A and FIG. 26B,the micro lens 355 a is of a parallel plate shape. Note that the x and ydirections in FIG. 26A are those as described previously. Asschematically illustrated in FIG. 26A, the micro lens 355 a has adiffraction grating formed therein at predetermined pitches. The microlens 355 a has a power of 0 in the x direction, and a positive power inthe y direction. The same advantageous effects as those obtained byemploying micro lens arrays constituted by the aforementioned microlenses 55 a or the micro lenses 55 a′ can be obtained by a micro lensarray constituted by the diffraction lenses 355 a.

In addition, a diffraction lens 455 a as illustrated in FIGS. 27A and27B may be employed instead of the aforementioned lens having positivepowers in both the x direction and the y direction, with the power inthe x direction being smaller than that in the y direction. FIGS. 27Aand 27B are a front view and a side view of the micro lens 455 a,respectively. As illustrated in FIGS. 27A and 27B, the diffraction lens455 a is of a parallel plate shape. Note that the x and y directions inFIG. 27A are those as described previously. As schematically illustratedin FIG. 27A, the diffraction grating of the micro lens 455 a has agreater pitch spacing in the y direction than in the x direction, andthe power in the x direction is configured to be smaller than the powerin the y direction. The same advantageous effects as those obtained byemploying micro lens arrays constituted by the aforementioned microlenses having positive powers in both the x direction and the ydirection, with the power in the x direction being smaller than that inthe y direction, can be obtained by a micro lens array constituted bythe diffraction lenses 455 a.

Further, combinations of at least two of: refractive lenses; gradientindex lenses; and diffraction lenses may be employed instead of theaforementioned micro lenses. A Fresnel lens is an example of acombination of a refractive lens and a diffraction lens. As anotherexample, a spherical lens having a refractive index distribution is acombination of a refractive lens and a gradient index lens. In the casethat this type of lens is employed, the surface shape and the refractiveindex distribution both correct aberrations due to distortions of thereflective surfaces of the micro mirrors.

Here, separated condensing positions will be described with reference toFIG. 22A. The light beams reflected by each micro mirror 62 spread andoverlap upstream of the micro lenses 55 a, as schematically illustratedby the overlapping ovals denoted by broken lines in FIG. 22A. Incontrast, the light beams reflected by adjacent micro mirror 62 arecondensed as separate light beams downstream of the micro lenses 55 a,as schematically illustrated by the separated ovals denoted by brokenlines in FIG. 22A. In FIG. 22B as well, the light beams reflected byeach micro mirror 62 are condensed as separate light beams downstream ofthe micro lenses 55 a.

That is, a predetermined range downstream of the micro lenses 55 aincludes separated condensing positions, at which the light beamsreflected by each micro mirror 62 are condensed as separate light beamsby the lens systems 52, 54, and the micro lenses 55 a.

In the present embodiment, the aperture array 59 is provided at aseparated condensing position within the range. The aperture array 59 isconfigured such that each aperture 59 a thereof only transmits lightbeams that propagate thereto via a corresponding micro lens 55 a.Thereby, entry of light beams which have been condensed by adjacentmicro lenses 55 a that do not correspond to the apertures 59 a, andentry of stray light beams can be prevented, thereby improving theextinction ratio of the image exposure apparatus. In addition, theaperture array 59 configured in this manner exhibits high lightutilization efficiency, and may also function to shape the crosssectional shapes of the light beams with the apertures 59 a.

Hereinafter, image exposure apparatuses according to other embodimentsof the present invention will be described. In the followingdescriptions and the drawings referenced thereby, only characteristicstructures and differences between previous embodiments will bedescribed in detail. Elements which are the same as those of previousembodiments will be denoted with the same reference numbers, anddescriptions thereof will be omitted, insofar as they are notparticularly necessary.

An image exposure apparatus according to a second embodiment of thepresent invention will be described next. FIG. 28 is a schematicsectional view that illustrates an exposure head of the image exposureapparatus according to the second embodiment of the present invention.The exposure head of FIG. 28 differs from the exposure head of the imageexposure apparatus according to the first embodiment illustrated in FIG.5 in that it comprises a focusing optical system 51′ instead of thefocusing optical system 51. The focusing optical system 51′ differs fromthe focusing optical system 51 in that the second focusing opticalsystem, comprising the lens systems 57 and 58, has been omitted. Theother structures are the same as those of the previously describedembodiment, and therefore detailed descriptions thereof will be omitted.

That is, in the second embodiment, light beams, which are condensed bythe micro lens array 55, directly expose the photosensitive material150. The second embodiment is capable of obtaining the same advantageouseffects as the first embodiment.

An image exposure apparatus according to a third embodiment of thepresent invention will be described next. FIG. 29 is a schematicsectional view that illustrates an exposure head of the image exposureapparatus according to the third embodiment of the present invention.The exposure head of FIG. 29 differs from the exposure head of the imageexposure apparatus according to the first embodiment illustrated in FIG.5 in that it further comprises a micro lens array 56 at a separatedcondensing position. The image exposure apparatus according to the thirdembodiment employs a focusing optical system 151 instead of the focusingoptical system 51 of the first embodiment. The focusing optical system151 comprises: the first focusing optical system comprising lens systems52 and 54; the second focusing optical system comprising the lenssystems 57 and 58; the micro lens array 55; the condensing micro lensarray 56; and an aperture array 159. The micro lens array 55, thecondensing micro lens array 56, and the aperture array 159 are providedbetween the first and second focusing optical systems. The otherstructures are the same as those of the previously described embodiment,and therefore detailed descriptions thereof will be omitted.

The condensing micro lens array 56 comprises a plurality of micro lenses56 a that individually condense the light beams from each pixel portion.Light beams, of which the aberration has been corrected by the microlenses 55 a of the micro lens array 55, enter the micro lenses 56 a. Inaddition, the aperture array 159 has a great number of apertures 159 a,corresponding to the micro lenses 56 a of the micro lens array 56,formed in a light shielding member, similar to the aperture array 59.The aperture array 159 is provided such that only light beams thatpropagate through the corresponding micro lens 56 a enter each aperture159 a.

The third embodiment is capable of obtaining the same advantageouseffects as the first embodiment. In addition, in the configurationdescribed above, the light beams, which have been condensed and of whichthe cross sectional shapes have been shaped by the micro lens array 55,are further condensed by the micro lens array 56. Therefore, the beamspot size can be controlled to be even smaller than in the firstembodiment, improving the sharpness of images to be exposed.

An image exposure apparatus according to a fourth embodiment of thepresent invention will be described next. FIG. 30 is a schematicsectional view that illustrates an exposure head of the image exposureapparatus according to the fourth embodiment of the present invention.The exposure head of FIG. 30 differs from the exposure head of the imageexposure apparatus according to the third embodiment illustrated in FIG.29 in that it comprises a focusing optical system 151′ instead of thefocusing optical system 151. The focusing optical system 151′ differsfrom the focusing optical system 151 in that the second focusing opticalsystem, comprising the lens systems 57 and 58, has been omitted. Theother structures are the same as those of the previously describedembodiment, and therefore detailed descriptions thereof will be omitted.

That is, in the fourth embodiment, light beams, which are condensed bythe micro lens array 55 and the micro lens array 56, directly expose thephotosensitive material 150. The fourth embodiment is capable ofobtaining the same advantageous effects as the third embodiment.

Further, the condensing micro lens array 56 may be provided to bemovable in the direction of the optical axes of the light beams. In thiscase, adjustments to the focal point of the light beams are facilitated.Particularly, because the condensing micro lens array 56 is provided atthe separated condensing position and not at the focusing position, thevariance in light utilization efficiency can be suppressed to a minimumwhen the focal point is adjusted. That is, the variance in lightutilization efficiency at the separated condensing position and thevicinity thereof is smaller than that at the focusing position and thevicinity thereof. Therefore, drastic changes in the light utilizationefficiency when the condensing micro lens array 56 is moved in thedirection of the optical axes can be prevented.

An image exposure apparatus according to a fifth embodiment of thepresent invention will be described next. FIG. 31 is a schematicsectional view that illustrates an exposure head of the image exposureapparatus according to the fifth embodiment of the present invention.The exposure head of FIG. 31 differs from the exposure head of the imageexposure apparatus according to the first embodiment illustrated in FIG.5 in that it employs a focusing optical system 251 instead of thefocusing optical system 51. The characteristic features of the imageexposure apparatus according to the fifth embodiment are that: micromirrors have powers of different signs in two directions within a planeperpendicular to the optical axis; a micro lens array 555 is provided ata separated condensing position; and each micro lens 555 a of the microlens array 555 has powers of different signs in two directions within aplane perpendicular to the optical axis, to correct aberrations causedby the powers of the micro mirrors.

The shapes of the micro mirrors 62 of the image exposure apparatusaccording to the fifth embodiment are the same as those of the firstembodiment, as illustrated in FIG. 18A and FIG. 18B. Note that FIG. 18Aand FIG. 18B are graphs that schematically illustrate the heightdisplacement of the reflective surface of a micro mirror 62 in planesparallel to the x direction and the y direction, respectively. Inaddition, the x and y directions are the same as those of the firstembodiment, illustrated in FIG. 17. As illustrated in FIG. 18A and FIG.18B, the reflective surface of the micro mirror 62 is a curved surfacehaving a concave shape in the x direction and a convex shape in theydirection. That is, the reflective surface is a rotationallyasymmetrical curved surface, and has an anisotropic distortion. Due tothis shape, the micro mirror 62 is of a rotationally asymmetricalstructure that has powers of different signs in the x direction and they direction.

If collimated light is irradiated onto the micro mirror 62 having thepowers of different signs as described above, the reflected light willbe convergent in the x direction and divergent in the y direction, asdescribed previously with reference to FIG. 19A and FIG. 19B.

In the case that light that converges in the x direction and diverges inthe y direction as described above is condensed by a normal lens, whichhas a power rotationally symmetrical with respect to the optical axis,the position in the direction of the optical axis at which the beamdiameter is minimal (beam waist position) is different in the xdirection and the y direction. That is, an astigmatic aberration occurs,which becomes an obstacle to obtaining highly detailed images.

In order to prevent the aforementioned problem, the micro lenses 555 aof the micro lens array 555 of the image exposure apparatus according tothe present embodiment are of shapes different from conventional microlenses. Hereinafter, this point will be described in detail.

The structure of the micro lens array 555 as a whole is the same as thatof the first embodiment illustrated in FIG. 20A and FIG. 20B, andtherefore a detailed description thereof will be omitted.

Each micro lens 555 a has different powers in the x direction and the ydirection, in order to correct the aforementioned anisotropic distortionof the reflective surface of the micro mirrors 62. That is, each microlens 555 a has a power which is rotationally asymmetric with respect tothe optical axis. More specifically, each micro lens 555 a of the fifthembodiment is a cylindrical lens having a power of 0 in the x direction,and a power of a positive value in the y direction, similar to thecylindrical lens of the first embodiment described with reference toFIGS. 21A, 21B, and 21C. The value of the power in the y direction isdetermined such that the difference in beam waist position (astigmaticdifference) in the x direction and the y direction after the laser beampasses through the lens systems 52 and 54 and the micro lenses 555 aapproximates 0, taking the curvature of the reflective surface of themicro mirror 62 into consideration.

The manner in which aberrations caused by the distortion in thereflective surfaces of the micro mirrors 62 is corrected by the microlenses 555 a will be described in greater detail. FIGS. 32A and 32B areschematic diagrams that illustrate the manner in which the lightreflected by the micro mirrors 62 are corrected within cross sectionsthat pass through the optical axis and are parallel to the x directionand the y direction, respectively.

Note that the TIR prism 70 is omitted from FIGS. 32A and 32B. Threeadjacent micro mirrors 62 are illustrated in FIGS. 32A and 32B, and thelight beams reflected by the center and the edges of the central micromirror 62 are denoted by solid lines. In addition, the manner in whichthe beam diameters of the beams reflected by the three micro mirrors 62change as the beams propagate downstream from the lens system 54 isdenoted by the ovals illustrated by broken lines.

Here, the effects of correction by the micro lenses 555 a of the fifthembodiment become clear, by comparing FIGS. 19A and 19B against FIGS.32A and 32B. In FIG. 19B, the light beams spread and overlap in the ydirection downstream of the focusing position of the micro mirrors 62,as schematically illustrated by the overlapping ovals denoted by brokenlines. In contrast, the light beams are condensed as separate lightbeams upstream of the focusing position of the micro mirrors 62, asschematically illustrated by the separated ovals denoted by broken linesin FIG. 19B. As illustrated in FIG. 32B, the micro lens array 555 isprovided at the separated condensing position.

As illustrated in FIG. 32A, the light, which is reflected by the micromirror 62 having the concave shape, becomes convergent light, and entersthe micro lens 555 a after passing through the lens systems 52 and 54.As described previously, the power of the micro lens 555 a in the xdirection is 0. Therefore, the light that enters the micro lens 555 apropagates without changing its angle with respect to the optical axisin the x direction, and the beam diameter thereof becomes minimal at itsbeam waist position.

Meanwhile, as illustrated in FIG. 32B, the light, which is reflected bythe micro mirror having the convex shape in the y direction, becomesdivergent light, and enters the micro lens 555 a after passing throughthe lens systems 52 and 54. As described previously, the micro lens 555a has a positive power in the y-direction. Therefore, the light thatenters the micro lens 555 a is condensed in the y direction, and thebeam diameter thereof becomes minimal at the same position as theaforementioned beam waist position of the x direction.

As described above, the micro lens 555 a is configured to have differentpowers in the x direction and the y direction. Thereby, astigmaticaberrations can be corrected, and the cross sectional shape of the beamcan be prevented from becoming oval, even if the reflective surface ofthe micro mirror 62 has powers of different signs in two directionswithin a plane perpendicular to the optical axis. Accordingly, the beamwaist positions in the x direction and the y direction are matched, thecross sectional shape of the beam can be shaped, and a condensed beamcan be utilized to form images. Therefore, obtainment of highly detailedimages becomes possible.

Note that the cross sectional shape of the micro lenses 555 a in the ydirection is not limited to the flat bottomed protrusion illustrated inFIG. 21C, and may be a meniscus shape. In addition, the power of themicro lenses in the direction that the reflective surfaces of the micromirrors are concave is 0 in the present embodiment. However, the presentinvention is not limited to this configuration. The micro lenses mayhave a positive or negative power in the direction that the reflectivesurfaces of the micro mirrors are concave, as long as the light becomesconvergent after passing through the micro lenses and astigmaticaberrations caused by the micro mirrors can be corrected. In addition,in the above description, the curved shape of the micro lenses isspherical. However, the present invention is not limited to thisconfiguration, and higher order (quartic, sextic, . . . ) asphericalshapes may be adopted.

The micro lenses 555 a of the micro lens array 555 of the fifthembodiment were described as refractive lenses. Alternatively, thegradient index lenses illustrated in FIGS. 23A, 23B, 24A, and 24B, thediffraction lens illustrated in FIGS. 26A and 26B, or combined lensesmay be employed, to obtain the same advantageous effects as thoseobtained by the aforementioned micro lenses 555 a.

Here, the manner in which reductions in light utilization efficiency andextinction ratio of the image exposure apparatus can be prevented in thecase that the micro lens array is provided at the separated condensingposition will be described with reference to FIGS. 33A, 33B, 34A, and34B.

The circular regions denoted by reference number 110 in FIG. 33A arebeam spots which have been reflected by the micro mirrors 62 and havepassed through the first optical system comprising the lens systems 52and 54. The rectangular region denoted by reference number 101 in FIG.33B illustrates a micro lens array 101, in which a plurality of microlenses 102 are provided.

The micro lenses 102 and the micro lens array 101 are equivalent to theaforementioned micro lenses 555 a and the micro lens array 555. Themicro lens array 101 is provided at a separated condensing position.

The aforementioned beam spots differ from images of pixel portions inthat they are beam spots of small sizes (condensed sizes). Therelationship between these beam spots and the micro lenses 102 of themicro lens array 101 is as illustrated in FIGS. 34A and 34B. That is,eclipsing of the beam spots and entrance of the beam spots into microlenses 102 adjacent to those that they are intended to enter areprevented, even if the spatial light modulating element and thecondensing micro lens array are shifted somewhat, as illustrated in FIG.34B, as well as in cases that the beam spot and the micro lens 102 areconcentric, as illustrated in FIG. 34A. Accordingly, reductions in thelight utilization efficiency and extinction ratio of the image exposureapparatus are prevented.

In the fifth embodiment, the aperture array 59 is provided at theseparated condensing position. The aperture array 59 is configured suchthat only light which has passed through a corresponding micro lens 555a enters each aperture 59 a thereof. Thereby, entry of light beams whichhave been condensed by adjacent micro lenses 555 a that do notcorrespond to the apertures 59 a, and entry of stray light beams can beprevented, thereby improving the extinction ratio of the image exposureapparatus. In addition, the aperture array 59 configured in this mannerexhibits high light utilization efficiency, and may also function toshape the cross section shapes of the light beams with the apertures 59a.

An image exposure apparatus according to a sixth embodiment of thepresent invention will be described next. FIG. 35 is a schematicsectional view that illustrates an exposure head of the image exposureapparatus according to the sixth embodiment of the present invention.The exposure head of FIG. 35 differs from the exposure head of the imageexposure apparatus according to the fifth embodiment illustrated in FIG.31 in that it comprises a focusing optical system 251′ instead of thefocusing optical system 251. The focusing optical system 251′ differsfrom the focusing optical system 251 in that the second focusing opticalsystem, comprising the lens systems 57 and 58, has been omitted. Thatis, in the second embodiment, light beams, which are condensed by themicro lens array 555, directly expose the photosensitive material 150.The sixth embodiment is capable of obtaining the same advantageouseffects as the fifth embodiment.

An image exposure apparatus according to a seventh embodiment of thepresent invention will be described next. FIG. 36 is a schematicsectional view that illustrates an exposure head of the image exposureapparatus according to the seventh embodiment of the present invention.The exposure head of FIG. 36 differs from the exposure head of the imageexposure apparatus according to the fifth embodiment illustrated in FIG.31 in that it further comprises a micro lens array 56 at a separatedcondensing position. The image exposure apparatus according to theseventh embodiment employs a focusing optical system 351 instead of thefocusing optical system 251 of the fifth embodiment. The focusingoptical system 351 comprises: the first focusing optical systemcomprising lens systems 52 and 54; the second focusing optical systemcomprising the lens systems 57 and 58; the micro lens array 555; thecondensing micro lens array 56; and an aperture array 159. The microlens array 555, the condensing micro lens array 56, and the aperturearray 159 are provided between the first and second focusing opticalsystems. The other structures are the same as those of the previouslydescribed embodiment, and therefore detailed descriptions thereof willbe omitted.

The condensing micro lens array 56 comprises a plurality of micro lenses56 a that individually condense the light beams from each pixel portion.Light beams, of which the aberration has been corrected by the microlenses 555 a of the micro lens array 555, enter the micro lenses 56 a.In addition, the aperture array 159 has a great number of apertures 159a, corresponding to the micro lenses 56 a of the micro lens array 56,formed in a light shielding member, similar to the aperture array 59.The aperture array 159 is provided such that only light beams thatpropagate through the corresponding micro lens 56 a enter each aperture159 a.

The seventh embodiment is capable of obtaining the same advantageouseffects as the fifth embodiment. In addition, in the configurationdescribed above, the light beams, which have been condensed and of whichthe cross sectional shapes have been shaped by the micro lens array 55,are further condensed by the micro lens array 56. Therefore, the beamspot size can be controlled to be even smaller than in the fifthembodiment, improving the sharpness of images to be exposed.

An image exposure apparatus according to an eighth embodiment of thepresent invention will be described next. FIG. 37 is a schematicsectional view that illustrates an exposure head of the image exposureapparatus according to the eighth embodiment of the present invention.The exposure head of FIG. 37 differs from the exposure head of the imageexposure apparatus according to the seventh embodiment illustrated inFIG. 36 in that it comprises a focusing optical system 351′ instead ofthe focusing optical system 351. The focusing optical system 351′differs from the focusing optical system 351 in that the second focusingoptical system, comprising the lens systems 57 and 58, has been omitted.That is, in the eighth embodiment, light beams, which are condensed bythe micro lens array 555 and the micro lens array 56, directly exposethe photosensitive material 150. The eighth embodiment is capable ofobtaining the same advantageous effects as the seventh embodiment.

Further, the condensing micro lens array 56 may be provided to bemovable in the direction of the optical axes of the light beams. In thiscase, adjustments to the focal point of the light beams are facilitated.Particularly, because the condensing micro lens array 56 is provided atthe separated condensing position and not at the focusing position, thevariance in light utilization efficiency can be suppressed to a minimumwhen the focal point is adjusted. That is, the variance in lightutilization efficiency at the separated condensing position and thevicinity thereof is smaller than that at the focusing position and thevicinity thereof. Therefore, drastic changes in the light utilizationefficiency when the condensing micro lens array 56 is moved in thedirection of the optical axes can be prevented.

An image exposure apparatus according to a ninth embodiment of thepresent invention will be described next. FIG. 38 is a sectional viewthat illustrates an exposure head of the image exposure apparatusaccording to the ninth embodiment of the present invention. The exposurehead of FIG. 38 differs from the exposure head of the image exposureapparatus according to the first embodiment illustrated in FIG. 5 inthat it employs a DMD 450 and a focusing optical system 451 instead ofthe DMD 50 and the focusing optical system 51. The characteristicfeatures of the image exposure apparatus according to the fifthembodiment are that: micro mirrors 462 have different powers of the samesign in two directions within a plane perpendicular to the optical axis;a micro lens array 655 is provided at a separated condensing position;and each micro lens 655 a of the micro lens array 555 has differentpowers in two directions within a plane perpendicular to the opticalaxis, to correct aberrations caused by the powers of the micro mirrors.

The shapes of the micro mirrors 462 of the image exposure apparatusaccording to the ninth embodiment are illustrated in FIG. 39A and FIG.39B. FIG. 39A and FIG. 39B are graphs that schematically illustrate theheight displacement of the reflective surface of a micro mirror 462 inplanes parallel to the x direction and the y direction, respectively. Inaddition, the x and y directions are the same as those of the firstembodiment, illustrated in FIG. 17. In FIG. 39A and FIG. 39B, thehorizontal axes of the graphs represent distances from the center of thereflective surface in the respective directions, and the vertical axesrepresent displacement in the direction of the optical axis. Asillustrated in FIG. 39A and FIG. 39B, the reflective surface of themicro mirror 462 is a convex curved surface in both the x direction andthe y direction. However, the radius of curvature is smaller in the xdirection than in the y direction, and the reflective surface has ananisotropic distortion. Due to this shape, the micro mirror 462 is of arotationally asymmetrical structure that has positive powers of in boththe x direction and the y direction, with the power in the x directionbeing greater than that in the y direction.

If collimated light is irradiated onto the micro mirror 462 having thedifferent powers as described above, the reflected light will beconvergent in both the x direction and the y direction. However themanner of convergence will differ in the x direction and the ydirection.

FIG. 40A and FIG. 40B are diagrams that illustrate how light reflectedby the aforementioned micro mirror 462 propagates through the lenssystems 52 and 54 that constitute the first focusing system, withinplanes parallel to the x direction and the y-direction, respectively.

Note that the TIR prism 70 and the micro lens array 655 are omitted fromFIG. 40A and FIG. 40B. Three adjacent micro mirrors 462 are illustratedin FIG. 40A and FIG. 40B. The images borne by the light reflected byeach of the micro mirrors 462 are denoted by the curved arrows, and thelight beams reflected by the center and the edges of the central micromirror 462 are denoted by solid lines. In addition, the manner in whichthe beam diameters of the beams reflected by the three micro mirrors 462change as the beams propagate downstream from the lens system 54 isdenoted by the ovals illustrated by broken lines in FIG. 40A and FIG.40B.

As illustrated in FIG. 40A and FIG. 40B, the light beam reflected by themicro mirrors 462 is condensed to a greater degree in the x directionthan in the y direction, and the beam waist position in the x directionis closer to the lens system 54 than the beam waist position in the ydirection. In the case that this light beam is condensed by a normallens, which has a power rotationally symmetrical with respect to theoptical axis, the beam waist position will be different in the xdirection and the y direction. That is, an astigmatic aberration occurs,which becomes an obstacle to obtaining highly detailed images.

In order to prevent the aforementioned problem, the micro lenses 655 aof the micro lens array 655 of the image exposure apparatus according tothe ninth embodiment are of shapes different from conventional microlenses. Hereinafter, this point will be described in detail.

The structure of the micro lens array 655 as a whole is the same as thatof the first embodiment illustrated in FIG. 20A and FIG. 20B, andtherefore a detailed description thereof will be omitted. Each microlens 655 a has different powers in the x direction and the y direction,in order to correct aberrations due to the aforementioned anisotropicdistortion of the reflective surface of the micro mirrors 462. That is,each micro lens 655 a is an anamorphic lens having rotationallyasymmetrical powers with respect to the optical axis. Cylindrical lensesand toric lenses are examples of anamorphic lenses.

In the ninth embodiment, each micro lens 655 a is a cylindrical lenshaving a power of 0 in the x direction, and a power of a positive valuein the y direction, similar to the cylindrical lens of the firstembodiment described with reference to FIGS. 21A, 21B, and 21C. Thevalue of the power in the y direction is determined such that thedifference in beam waist position (astigmatic difference) in the xdirection and the y direction after the laser beam passes through thelens systems 52 and 54 and the micro lenses 555 a approximates 0, takingthe curvature of the reflective surface of the micro mirror 62 intoconsideration.

The manner in which aberrations caused by the distortion in thereflective surfaces of the micro mirrors 462 is corrected by the microlenses 655 a will be described in greater detail. FIGS. 41A and 41B areschematic diagrams that illustrate the manner in which the lightreflected by the micro mirrors 462 are corrected within cross sectionsthat pass through the optical axis and are parallel to the x directionand the y direction, respectively.

Note that the TIR prism 70 is omitted from FIGS. 41A and 41B. Threeadjacent micro mirrors 462 are illustrated in FIGS. 41A and 41B. Theimages borne by the light reflected by each of the micro mirrors 462 aredenoted by the curved arrows, and the light beams reflected by thecenter and the edges of the central micro mirror 462 are denoted bysolid lines. In addition, the manner in which the beam diameters of thebeams reflected by the three micro mirrors 462 change as the beamspropagate downstream from the lens system 54 is denoted by the ovalsillustrated by broken lines.

In FIG. 41A and FIG. 41B, the light beams overlap upstream of thefocusing position of the micro mirrors 462, as schematically illustratedby the overlapping ovals denoted by broken lines. In contrast, the lightbeams are condensed as separate light beams within a predetermined rangedownstream of the focusing position of the micro mirrors 462, asschematically illustrated by the separated ovals denoted by broken linesin FIG. 41A and FIG. 41B. The micro lens array 655 is provided at aseparated condensing position within the predetermined range.

As illustrated in FIG. 41A, the light, which is reflected by the micromirror 462 having the concave shape, becomes convergent light, andenters the micro lens 655 a after passing through the lens systems 52and 54. As described previously, the power of the micro lens 655 a inthe x direction is 0. Therefore, the light that enters the micro lens655 a propagates without changing its angle with respect to the opticalaxis in the x direction, and the beam diameter thereof becomes minimalat its beam waist position.

Meanwhile, as illustrated in FIG. 41B, the light, which is reflected bythe micro mirror 462 having the concave shape with a greater radius ofcurvature in the y direction, becomes convergent light, and enters themicro lens 655 a after passing through the lens systems 52 and 54.However, the angle formed by the light beam with respect to the opticalaxis is smaller than that in the x direction. As described previously,the micro lens 655 a has a positive power in the y direction. Therefore,the light that enters the micro lens 655 a is condensed in the ydirection, and the beam diameter thereof becomes minimal at the sameposition as the aforementioned beam waist position of the x direction.

As described above, the micro lens 555 a is configured to have differentpowers in the x direction and the y direction. Thereby, astigmaticaberrations can be corrected, and the cross sectional shape of the beamcan be prevented from becoming oval, even if the reflective surface ofthe micro mirror 462 has different powers in two directions within aplane perpendicular to the optical axis. Accordingly, the beam waistpositions in the x direction and the y direction are matched, the crosssectional shape of the beam can be shaped, and a condensed beam can beutilized to form images. Therefore, obtainment of highly detailed imagesbecomes possible.

In the above embodiment, an example was described in which thereflective surface of the micro mirror 462 had positive powers in boththe x direction and the y direction. It is possible to correctastigmatic aberrations in the case that a micro mirror has differentnegative powers in the x direction and the y direction, by employing ananamorphic micro lens in a similar manner. This case will be describednext.

An example will be described in which a DMD 550, comprising micromirrors 562 having anisotropic distortions is employed to form images.The micro mirrors 562 is of a convex shape in both the x direction andthe y direction, wherein the radius of curvature is greater in the xdirection than in the y direction. Due to the shape of the micro mirrors562, a micro mirror 562 is of a rotationally asymmetric shape havingnegative powers in both the x direction and the y direction, wherein theabsolute value of the power in the x direction is less than the absolutevalue of the power in the y direction.

In this case, a micro lens array 755 comprising a plurality of microlenses 755 a is employed instead of the micro lens array 655 comprisingthe micro lenses 655 a. Each of the micro lenses 755 a has positivepowers in both the x direction and the y direction, wherein the power inthe x direction is smaller than the power in the y direction.

FIG. 42A and FIG. 42B are a front view and a side view of a toric lensthat has powers as described above. Note that contour lines of the microlens 755 a are illustrated in FIG. 42A. FIG. 43A and FIG. 43Bschematically illustrate the states of the collimated laser beam B whenit passes through the micro lens 755 a in cross sections parallel to thex direction and the y direction, respectively. That is, when the crosssection parallel to the x direction and the cross section parallel tothe y direction are compared, the radius of curvature of the micro lens755 a is smaller in the y direction, which results in a shorter focaldistance.

More specifically, the values of the power in the x and y directions aredetermined such that the difference in beam waist position (astigmaticdifference) in the x direction and the y direction after the laser beamis reflected by the micro mirror 562 and passes through the lens systems52 and 54 and the micro lenses 755 a approximates 0, taking thecurvature of the reflective surface of the micro mirror 562 intoconsideration.

The manner in which aberrations caused by the distortion in thereflective surfaces of the micro mirrors 562 is corrected by the microlenses 755 a will be described with reference to FIG. 44A and FIG. 44B.FIGS. 44A and 44B are schematic diagrams that illustrate the manner inwhich the light reflected by the micro mirrors 562 are corrected withincross sections that pass through the optical axis and are parallel tothe x direction and the y direction, respectively.

Note that the TIR prism 70 is omitted from FIGS. 44A and 44B. Threeadjacent micro mirrors 562 are illustrated in FIGS. 44A and 44B, and thelight beams reflected by the center and the edges of the central micromirror 562 are denoted by solid lines. In addition, the manner in whichthe beam diameters of the beams reflected by the three micro mirrors 562change as the beams propagate downstream from the lens system 54 isdenoted by the ovals illustrated by broken lines.

In FIG. 44A and FIG. 44B, the positions upstream of the focusingposition of the micro mirrors 562 are the separated condensing positionsdue to the convex shape thereof, as schematically illustrated by theseparated ovals denoted by broken lines in FIG. 44A and FIG. 44B. Themicro lens array 755 is provided at a separated condensing position.

As illustrated in FIG. 44A, the light, which is reflected by the micromirror 562 having the convex shape, becomes divergent light, and entersthe micro lens 755 a after passing through the lens systems 52 and 54.As described previously, the power of the micro lens 655 a in the xdirection is positive. Therefore, the light that enters the micro lens755 a is condensed, and the beam diameter thereof becomes minimal at itsbeam waist position.

Meanwhile, as illustrated in FIG. 44B, the light, which is reflected bythe micro mirror 562 having the convex shape with a smaller radius ofcurvature in the y direction, also becomes divergent light, and entersthe micro lens 755 a after passing through the lens systems 52 and 54.However, the angle formed by the light beam with respect to the opticalaxis is greater than that in the x direction. As described previously,the micro lens 755 a has a positive power in the y direction, which isgreater than the power in the x direction. Therefore, the light thatenters the micro lens 755 a is condensed more intensely in the ydirection, and the beam diameter thereof becomes minimal at the sameposition as the aforementioned beam waist position of the x direction.

As described above, the micro lens 755 a is configured to have powers ofdifferent magnitudes in the x direction and they direction. Thereby,astigmatic aberrations can be corrected, and the cross sectional shapeof the beam can be prevented from becoming oval, even if the reflectivesurface of the micro mirror 562 has different negative powers in twodirections within a plane perpendicular to the optical axis.Accordingly, the same advantageous effects as those of the previouslydescribed configuration can be obtained with this configuration.

Note that in the above description, the micro lenses 655 a weredescribed as cylindrical lenses having power only in the y direction.However, the present invention is not limited to this configuration.Lenses having powers other than 0 in both the x direction and the ydirection may be used, wherein the power in the x direction is smallerthan the power in the y direction. For example, a toric lens such asthat illustrated in FIGS. 42A, 42B, 43A, and 43B may be employed. Inaddition, the shapes of the micro lenses in each direction are notlimited to being spherical, and may be of aspherical shapes.

The micro lenses 655 a and 755 a of the micro lens arrays 655 and 755 ofthe ninth embodiment were described as refractive lenses. Alternatively,the gradient index lenses illustrated in FIGS. 23A, 23B, 24A, and 24B,the diffraction lens illustrated in FIGS. 26A and 26B, or combinedlenses may be employed, to obtain the same advantageous effects as thoseobtained by the aforementioned micro lenses 655 a and 755 a.

Note that as described in the fifth embodiment with reference to FIG. 33and FIG. 34, reductions in the light utilization efficiency andextinction ratio of the image exposure apparatus can prevented, in thecase that another micro lens array is provided at the separatedcondensing position.

In addition, the aperture array 59 is provided in the separatedcondensing position in the ninth embodiment, in a manner similar to thatof the fifth embodiment. The aperture array 59 is configured such thatonly light which has passed through the corresponding micro lens 655 aor 755 a enter each of the apertures 59 a. Thereby, entry of light beamswhich have been condensed by adjacent micro lenses 655 a and 755 a thatdo not correspond to the apertures 59 a, and entry of stray light beamscan be prevented, thereby improving the extinction ratio of the imageexposure apparatus. In addition, the aperture array 59 configured inthis manner exhibits high light utilization efficiency, and may alsofunction to shape the cross sectional shapes of the light beams with theapertures 59 a.

An image exposure apparatus according to a tenth embodiment of thepresent invention will be described next. FIG. 45 is a schematicsectional view that illustrates an exposure head of the image exposureapparatus according to the tenth embodiment of the present invention.The exposure head of FIG. 45 differs from the exposure head of the imageexposure apparatus according to the ninth embodiment illustrated in FIG.38 in that it comprises a focusing optical system 451′ instead of thefocusing optical system 451. The focusing optical system 451′ differsfrom the focusing optical system 451 in that the second focusing opticalsystem, comprising the lens systems 57 and 58, has been omitted. Thatis, in the tenth embodiment, light beams, which are condensed by themicro lens array 655, directly expose the photosensitive material 150.The tenth embodiment is capable of obtaining the same advantageouseffects as the ninth embodiment.

An image exposure apparatus according to an eleventh embodiment of thepresent invention will be described next. FIG. 46 is a schematicsectional view that illustrates an exposure head of the image exposureapparatus according to the eleventh embodiment of the present invention.The exposure head of FIG. 46 differs from the exposure head of the imageexposure apparatus according to the ninth embodiment illustrated in FIG.38 in that it further comprises a micro lens array 56 at a separatedcondensing position. The image exposure apparatus according to theeleventh embodiment employs a focusing optical system 551 instead of thefocusing optical system 451 of the ninth embodiment. The focusingoptical system 551 comprises: the first focusing optical systemcomprising lens systems 52 and 54; the second focusing optical systemcomprising the lens systems 57 and 58; the micro lens array 655; thecondensing micro lens array 56; and an aperture array 159. The microlens array 655, the condensing micro lens array 56, and the aperturearray 159 are provided between the first and second focusing opticalsystems.

The condensing micro lens array 56 comprises a plurality of micro lenses56 a that individually condense the light beams from each pixel portion.Light beams, of which the aberration has been corrected by the microlenses 655 a of the micro lens array 655, enter the micro lenses 56 a.In addition, the aperture array 159 has a great number of apertures 159a, corresponding to the micro lenses 56 a of the micro lens array 56,formed in a light shielding member, similar to the aperture array 59.The aperture array 159 is provided such that only light beams thatpropagate through the corresponding micro lens 56 a enter each aperture159 a.

The eleventh embodiment is capable of obtaining the same advantageouseffects as the ninth embodiment. In addition, in the configurationdescribed above, the light beams, which have been condensed and of whichthe cross sectional shapes have been shaped by the micro lens array 655,are further condensed by the micro lens array 56. Therefore, the beamspot size can be controlled to be even smaller than in the firstembodiment, improving the sharpness of images to be exposed.

An image exposure apparatus according to a twelfth embodiment of thepresent invention will be described next. FIG. 46 is a schematicsectional view that illustrates an exposure head of the image exposureapparatus according to the twelfth embodiment of the present invention.The exposure head of FIG. 46 differs from the exposure head of the imageexposure apparatus according to the eleventh embodiment illustrated inFIG. 45 in that it comprises a focusing optical system 551′ instead ofthe focusing optical system 551. The focusing optical system 551′differs from the focusing optical system 551 in that the second focusingoptical system, comprising the lens systems 57 and 58, has been omitted.That is, in the twelfth embodiment, light beams, which are condensed bythe micro lens array 655 and the micro lens array 56, directly exposethe photosensitive material 150. The twelfth embodiment is capable ofobtaining the same advantageous effects as the eleventh embodiment.

Further, the condensing micro lens array 56 may be provided to bemovable in the direction of the optical axes of the light beams. In thiscase, adjustments to the focal point of the light beams are facilitated.Particularly, because the condensing micro lens array 56 is provided atthe separated condensing position and not at the focusing position, thevariance in light utilization efficiency can be suppressed to a minimumwhen the focal point is adjusted. That is, the variance in lightutilization efficiency at the separated condensing position and thevicinity thereof is smaller than that at the focusing position and thevicinity thereof. Therefore, drastic changes in the light utilizationefficiency when the condensing micro lens array 56 is moved in thedirection of the optical axes can be prevented.

Note that the diagonals of the micro mirrors were designated as the xdirection and the y direction in the first through twelfth embodimentsdescribed above, and the micro lenses were configured to have differentpowers along these directions. However, it is desirable for thedesignation of the x and y directions to be determined according to thedistribution of distortion of the micro mirrors. For example, in thecase that conspicuously different curved surfaces are present along thedirections of the edges of the micro mirror, it is desirable for themicro lenses to have different powers along the directions of the edges.

In addition, the laser light source was employed as the light source forirradiating the spatial light modulating element in the first throughtwelfth embodiments described above. However, the present invention isnot limited to this configuration, and other light sources, such as amercury halide lamp, may alternatively be employed.

Further, the DMD's were employed as the spatial light modulating elementin the first through twelfth embodiments described above. However, thesame advantageous effects can be obtained by applying the structures ofthe present invention to image exposure apparatuses that employreflective spatial light modulating elements other than DMD's.

1-11. (canceled)
 12. An image exposure apparatus, comprising: a spatiallight modulating element, in which a plurality of pixel portions forindividually modulating light irradiated thereon according to controlsignals are provided; a light source, for irradiating light onto thespatial light modulating element; and a focusing optical system forfocusing an image borne by light modulated by each pixel portion of thespatial light modulating element onto a photosensitive material,including: an optical system for focusing light beams which have beenmodulated by each of the pixel portions of the spatial light modulatingelement, to focus the image of each pixel portion; and a micro lensarray, in which a plurality of micro lenses into which the light beamsmodulated by the pixel portions and passed through the optical systementer individually are provided; the micro lens array being provided inthe vicinity of the position at which the images of the pixel portionsare focused by the optical system; and each micro lens of the micro lensarray having different powers in two directions within a planeperpendicular to the optical axis of the light beam that entersthereinto, in order to correct aberrations due to isotropic distortionsof the pixel portions.
 13. An image exposure apparatus as defined inclaim 12, wherein: the micro lenses are refractive lenses.
 14. An imageexposure apparatus as defined in claim 12, wherein: the micro lenses aregradient index lenses.
 15. An image exposure apparatus as defined inclaim 12, wherein: the micro lenses are diffraction lenses.
 16. An imageexposure apparatus as defined in claim 12, wherein: the micro lenses arestructured by combining at least two of: refractive lenses; gradientindex lenses; and diffraction lenses.
 17. An image exposure apparatus asdefined in claim 12, further comprising: a condensing micro lens array,in which a plurality of micro lenses for individually condensing thelight beams which have propagated thereto via each of the pixel portionsare provided, is provided at a separated condensing position of thepixel portions, the optical system, and the micro lens array, which isoffset from a position at which the images of the pixel portions arefocused by the optical system.
 18. An image exposure apparatus,comprising: a spatial light modulating element, in which a plurality ofpixel portions for individually modulating light irradiated thereonaccording to control signals are provided; a light source, forirradiating light onto the spatial light modulating element; and afocusing optical system for focusing an image borne by light modulatedby each pixel portion of the spatial light modulating element onto aphotosensitive material, including: an optical system for focusing lightbeams which have been modulated by each of the pixel portions of thespatial light modulating element, to focus the image of each pixelportion; and a micro lens array, in which a plurality of micro lensesinto which the light beams modulated by the pixel portions and passedthrough the optical system enter individually are provided; the pixelportions having powers of different signs in two directions within aplane perpendicular to the optical axis of the light beam; the microlens array being provided at a separated condensing position, which isoffset from a position at which the images of the pixel portions arefocused by the optical system; and each micro lens of the micro lensarray having different powers in two directions within a planeperpendicular to the optical axis of the light beam that entersthereinto, in order to correct aberrations due to the powers ofdifferent signs of the pixel portions.
 19. An image exposure apparatusas defined in claim 18, wherein: the micro lenses are refractive lenses.20. An image exposure apparatus as defined in claim 18, wherein: themicro lenses are gradient index lenses.
 21. An image exposure apparatusas defined in claim 18, wherein: the micro lenses are diffractionlenses.
 22. An image exposure apparatus as defined in claim 18, wherein:the micro lenses are structured by combining at least two of: refractivelenses; gradient index lenses; and diffraction lenses.
 23. An imageexposure apparatus as defined in claim 18, further comprising: acondensing micro lens array, in which a plurality of micro lenses forindividually condensing the light beams which have propagated theretovia each of the pixel portions are provided, is provided at a separatedcondensing position of the pixel portions, the optical system, and themicro lens array, which is offset from a position at which the images ofthe pixel portions are focused by the optical system.
 24. An imageexposure apparatus, comprising: a spatial light modulating element, inwhich a plurality of pixel portions for individually modulating lightirradiated thereon according to control signals are provided; a lightsource, for irradiating light onto the spatial light modulating element;and a focusing optical system for focusing an image borne by lightmodulated by each pixel portion of the spatial light modulating elementonto a photosensitive material, including: an optical system forfocusing light beams which have been modulated by each of the pixelportions of the spatial light modulating element, to focus the image ofeach pixel portion; and a micro lens array, in which a plurality ofmicro lenses into which the light beams modulated by the pixel portionsand passed through the optical system enter individually are provided;the pixel portions having powers of the same sign and differentmagnitudes in two directions within a plane perpendicular to the opticalaxis of the light beam; the micro lens array being provided at aseparated condensing position, which is offset from a position at whichthe images of the pixel portions are focused by the optical system; andeach micro lens of the micro lens array having different powers in twodirections within a plane perpendicular to the optical axis of the lightbeam that enters thereinto, in order to correct aberrations due to thepowers of different magnitudes of the pixel portions.
 25. An imageexposure apparatus as defined in claim 24, wherein: the micro lenses arerefractive lenses.
 26. An image exposure apparatus as defined in claim24, wherein: the micro lenses are gradient index lenses.
 27. An imageexposure apparatus as defined in claim 24, wherein: the micro lenses arediffraction lenses.
 28. An image exposure apparatus as defined in claim24, wherein: the micro lenses are structured by combining at least twoof: refractive lenses; gradient index lenses; and diffraction lenses.29. An image exposure apparatus as defined in claim 24, furthercomprising: a condensing micro lens array, in which a plurality of microlenses for individually condensing the light beams which have propagatedthereto via each of the pixel portions are provided, is provided at aseparated condensing position of the pixel portions, the optical system,and the micro lens array, which is offset from a position at which theimages of the pixel portions are focused by the optical system.